Mermaid Sheet Cake (Beautiful Beginner Recipe)

If you’ve got a mermaid birthday party coming up, do you want to make a cake that’s sure to impress and make a real splash on your dessert table? This mermaid sheet cake is perfect for so many reasons. It’s bright, fun plus it’s beginner friendly. 

If it’s your first time making a birthday cake, it can be disappointing when the frosting doesn’t smooth out perfectly, or your cake breaks apart when you try to get it out of the pan. This cake takes away both those problems. It still looks great in the pan, just scoop out a slice when you’re ready to serve (and you can skip the cake board). The icing looks like wavy ocean waters, so say goodbye to the frustration of smoothing it out!

Get ready to be dazzled by swirls of color, magical mermaid tail chocolates and edible sand that will make your tastebuds dance with delight. This cake is absolutely fin-tastic for a mermaid party. Put on your mermaid flippers, grab your spatula and get ready to dive into a colorful world under the sea!

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For more recipe ideas that fit a mermaid theme, check out these other mermaid ideas like these Mermaid Cupcakes, these Mermaid Rice Krispy Treats, these Chocolate Covered Mermaid Pretzel Rods, and this easy chocolate Mermaid Bark for your next party!

Mermaid Sheet Cake Materials and Ingredients

Cake Mix

For this easy mermaid cake, I used a white box cake mix and you can too. You can also use your favorite vanilla cake recipe from scratch, I just wanted to keep it as easy as possible and you still end up with a delicious cake. You’ll also need blue and pink food coloring. I used Wilton Color Right Food Color System drops. You can get a full box set of colors with a color guide to help you mix colors perfectly.

Frosting

Here’s the one thing you don’t want to compromise on, you should try to make your own buttercream frosting for this cake. The cans of icing from the store will be too sticky and if you put it in a piping bag with a piping tip, it won’t look defined or sturdy. I used one cup of unsalted butter and 4 cups of powdered sugar with 2 teaspoons of vanilla and 2 tablespoons of whipping cream.

Decorations

To make the chocolate mermaid tails you’ll need a silicone candy mold. This is the mermaid tail mold I used. You’ll need chocolate candy melting wafers, either white, pink, or both. The beachy-looking sand is made of brown sugar. I also used mermaid sprinkles and edible glitter or ‘luster dust’, which are optional but a nice touch. For another option, I also used a second ocean-themed chocolate candy mold I had at home in the shape of seashells and sea creatures.

You can sometimes buy edible mermaid tail cake toppers at a craft or baking supply store if you’d prefer not to make your own like I did. 

Cake Pan

You can use a regular 9×13 cake pan to make a standard sheet cake, or use a 9×13 glass baking dish if you plan on leaving the cake inside like I did. 

Technically, a sheet cake is a rectangle of cake that comes out of the pan. If you’re comfortable with baking, and the idea of getting your cake out of a pan is no big deal, you can use a regular 9×13 cake pan and line it with parchment paper or use a baking release spray and follow all the other steps in this recipe. 

For this beginner recipe, we’re leaving the sheet cake inside a 9×13 glass baking dish to make it even simpler. You don’t need a cake board. You don’t need to frost the side of the cake. It’s easily transported to your birthday location. AND, it won’t crumble because you’re not taking it out the pan.

How to make an easy mermaid sheet cake

Make Chocolate Mermaid Tails

Melt Chocolate

Melt your white chocolate candy melts according to your package directions,either in a microwave safe dish in the microwave at 50% power, or low power, or use a double boiler on your stove.

I used plain white on its own for some of the tails. I also make some light pink mermaid tails by adding a touch of pink candy melts into more white candy melts to get the color I wanted.

Pipe Chocolate Into Mermaid Tail Mold

To give my chocolate mermaid tails a dual-tone color, I used edible glitter called luster dust and a brand new paint brush to coat the inside of my candy mold first, before using a plastic bag to pipe the melted chocolate inside. 

Use either a piping bag or a disposable plastic bag with the tip cut off to get your melted candy chocolate into the mermaid mold. You can also use a toothpick to help spread chocolate into the edges. 

Cool And De-mold Mermaid Tails

Let your chocolate mermaid tails cool completely to room temperature. The smallest point of your chocolate mermaid tails will be the most prone to breaking, so go slow and take your time. Pull the mold away from the candy to release it, then press the thickest spot out slowly.

To avoid breakage, I made my tails thicker in the narrow point of the mold so it overflows a little bit (which looks a bit lumpy on the back-side but no one will see it). 

Bake Cake

Make your cake batter according to your box cake directions then separate the cake batter into 3-4 smaller bowls to add food coloring. You don’t need a lot of dye to get light or pastel colors. I added half a drop of blue to get a light blue color. I added half a drop of blue and one drop of pink to get the purple colored cake batter. I added one drop of pink to get the pink cake batter. 

Grease your pan with butter or oil, then spoon small dollops of each color cake batter into your pan. For a nice colorful mermaid effect, use small spoonfuls to cover the entire pan, then if you have batter left over, add alternating colors on top so every slice has more than one color. 

Make Frosting

Make your vanilla buttercream frosting with 1 cup of unsalted butter and about 4 cups of icing sugar, 2 tsp of vanilla extract and 2 Tbs of cream or whole milk. Mix the ingredients in a large bowl with a hand mixer or stand mixer until they are completely blended and no sugar crystals remain.

Separate your white frosting into two bowls. Take about ½ a cup of white frosting in a small bowl and add a drop of pink food coloring and half a drop of blue; this should give you a light purple color of frosting. 

In the other large bowl of white frosting, add half a drop of blue food coloring. You can always add more but start small and see if you like the shade of blue first. This color will be used to frost your entire cake, so you need more of it. 

Scoop out ⅓ cup of the blue frosting and add another half drop of blue food coloring to make it a darker color for decorating with later.

Use your spoon or cake spatula to scoop your mermaid frosting into piping bags. Cut the tip of your piping bag off and put your metal piping tip inside then add your frosting.

For the light purple frosting, use a large open star tip like a Wilton brand #4B tip. For the dark blue, I used tip #96. 

Make Cake Number

To put a large number on a birthday cake like this, use parchment paper or wax paper to create an outline. I used a pen to make a dotted outline until I was happy with the shape, then drew in the lines and cut it out. Use whatever birthday number you’d like, or something different like a heart, initial or mermaid tail shape.

I also used the parchment paper to lay out my mermaid chocolates so I was happy with the look of it before I placed them on my cake. I just took a photo and copied the photo when I was decorating.

Decorate Cake

First, spread light blue buttercream frosting over the top of your mermaid cake using a cake spatula. It doesn’t need to be smooth; the lines going across look like ocean waves. 

Let the blue frosting set for a couple of minutes so it’s less sticky, then place your number made of parchment paper on top of the cake. Use a butter knife to score lightly around the edge of your number to create an outline and remove the paper.

Then use light brown sugar to create a thin layer of ‘sand’ inside your number outline. You can also use crushed graham crackers instead of brown sugar if you prefer. 

Add swirls and dots of purple and dark blue frosting to your cake with your piping bags and tips. Press down lightly, squeeze out some frosting, then stop squeezing and pull your bag away. Start in alternating corners and create a pattern you like, or make it random. 

Keep filling in the edge of your cake with decorations until you’re happy with how it looks.

Add your chocolate mermaid tails (and other seashells if you also have that second candy mold and made them, too).

Then add your finishing touches of frosting and a dash of mermaid themed sprinkles on top of the cake. 

Mermaid Cake Troubleshooting

Chocolate mermaid tails keep breaking

If you’re having trouble getting your cooled chocolate mermaid tails out of their mold, try pulling the silicone away from the chocolate first and moving slowly when popping them out of their mold. 

If your tails are always breaking at the same point, try making your chocolate thicker at that point of the mold. It may make the back of your chocolate a bit more lumpy but no one will see it.

How do you make chocolate mermaid tails two-tone?

I used edible luster dust to give my pink candy melts a purple tone. 

Put a layer of luster dust into your candy mold. Spread it around with a clean paint brush or tiny bit of paper towel. Then add your melted chocolate.

I can’t find mermaid themed sprinkles

You can make your own mix of sprinkles at home if you can’t find pre-packaged mermaid sprinkles. Use a combination of sprinkle colors like blue sanding sugar, small gold sugar balls, blue and purple jimmies, and teal colored sprinkles for a nice underwater vibe.

Check your local craft store in the baking section. You can also check Etsy and Amazon for mermaid-themed sprinkles if you have the time to order them.

Which steps can I prepare in advance?

You can make your chocolate mermaid tails up to a week before your event. Store them in an airtight container in a cool spot and they will still be fresh for decorating.

You can also prepare the number outline in advance and bake your cake the night before your party as long as it’s covered with plastic wrap so it doesn’t dry out. This way, the day of your party all you have to do is put on the frosting and decorate.

What can I do with extra melted chocolate candy melts?

If you melted too many candy melts and don’t want them to go to waste, spread the mixture out on some parchment paper and add mermaid sprinkles on top. Check out my recipe for Mermaid Bark and add it to your dessert table!

Final Thoughts on Mermaid Sheet Cakes

Whoever you’re making this mermaid sheet cake for sure is a lucky little mermaid! I hope they love it as much as the kids in my life did. If you’re making this cake for a baby shower instead of a mermaid birthday cake, try using an initial or mermaid tail shape or heart instead of a number for the brown sugar ‘sand’ center. 

For another easy and impressive dessert, check out this Triple Berry Trifle that uses store-bought angel food cake!

Share this recipe with someone who would love it and check out more mermaid themed treats from Mama’s Buzz like these Mermaid Cupcakes, these Mermaid Rice Krispie Treats, these Chocolate Covered Mermaid Pretzel Rods, and this easy chocolate Mermaid Bark!

Mermaid Cake

This beautiful mermaid sheet cake is easy enough for even a total beginner to make. Use the photo instructions to take you step-by-step to make a colorful cake inside and out that's sure to make a splash on your dessert table for next mermaid party.

Print Recipe Pin Recipe

Prep Time 1 hour hr 15 minutes mins

Cook Time 30 minutes mins

Total Time 1 hour hr 45 minutes mins

Course Dessert

Cuisine American

Servings 24

Calories 250 kcal

Equipment

• Parchment paper
• Scissors
• Pen
• 9×13 baking pan
• Cake spatula
• Mixing bowls
• Microwave safe bowls
• piping bags
• #4B & #96 piping tips
• Mermaid tail candy mold

Ingredients

  

• One box white cake mix
• Three eggs
• ½ cup Oil
• One cup water
• 1 cup Butter
• 4 cups Icing sugar
• 1 tsp Vanilla
• 2 tsp Heavy cream or milk
• Pink food coloring
• Blue food coloring
• Pink chocolate candy melts
• White chocolate candy melts
• Purple edible luster dust optional
• Brown sugar
• Mermaid sprinkles

Instructions

 

Make Chocolate Mermaid Tails

• Melt Chocolate
• Melt your white chocolate candy melts according to your package directions,either in a microwave safe dish in the microwave at 50% power, or low power, or use a double boiler on your stove.
• I used plain white on its own for some of the tails. I also make some light pink mermaid tails by adding a touch of pink candy melts into more white candy melts to get the color I wanted.
• Pipe Chocolate Into Mermaid Tail Mold
• To give my chocolate mermaid tails a dual-tone color, I used edible glitter called luster dust and a brand new paint brush to coat the inside of my candy mold first, before using a plastic bag to pipe the melted chocolate inside.
• Use either a piping bag or a disposable plastic bag with the tip cut off to get your melted candy chocolate into the mermaid mold. You can also use a toothpick to help spread chocolate into the edges.
• Cool And De-mold Mermaid Tails
• Let your chocolate mermaid tails cool completely to room temperature. The smallest point of your chocolate mermaid tails will be the most prone to breaking, so go slow and take your time. Pull the mold away from the candy to release it, then press the thickest spot out slowly.
• To avoid breakage, I made my tails thicker in the narrow point of the mold so it overflows a little bit (which looks a bit lumpy on the back-side but no one will see it).

Bake Cake

• Make your cake batter according to your box cake directions then separate the cake batter into 3-4 smaller bowls to add food coloring. You don’t need a lot of dye to get light or pastel colors. I added half a drop of blue to get a light blue color. I added half a drop of blue and one drop of pink to get the purple colored cake batter. I added one drop of pink to get the pink cake batter.
• Grease your pan with butter or oil, then spoon small dollops of each color cake batter into your pan. For a nice colorful mermaid effect, use small spoonfuls to cover the entire pan, then if you have batter left over, add alternating colors on top so every slice has more than one color.

Make Frosting

• Make your vanilla buttercream frosting with 1 cup of unsalted butter and about 4 cups of icing sugar, 2 tsp of vanilla extract and 2 Tbs of cream or whole milk. Mix the ingredients in a large bowl with a hand mixer or stand mixer until they are completely blended and no sugar crystals remain.
• Separate your white frosting into two bowls. Take about ½ a cup of white frosting in a small bowl and add a drop of pink food coloring and half a drop of blue; this should give you a light purple color of frosting.
• In the other large bowl of white frosting, add half a drop of blue food coloring. You can always add more but start small and see if you like the shade of blue first. This color will be used to frost your entire cake, so you need more of it.
• Scoop out ⅓ cup of the blue frosting and add another half drop of blue food coloring to make it a darker color for decorating with later.
• Use your spoon or cake spatula to scoop your mermaid frosting into piping bags. Cut the tip of your piping bag off and put your metal piping tip inside then add your frosting.
• For the light purple frosting, use a large open star tip like a Wilton brand #4B tip. For the dark blue, I used tip #96.

Make Cake Number

• To put a large number on a birthday cake like this, use parchment paper or wax paper to create an outline. I used a pen to make a dotted outline until I was happy with the shape, then drew in the lines and cut it out. Use whatever birthday number you’d like, or something different like a heart, initial or mermaid tail shape.
• I also used the parchment paper to lay out my mermaid chocolates so I was happy with the look of it before I placed them on my cake. I just took a photo and copied the photo when I was decorating.

Decorate Cake

• First, spread light blue buttercream frosting over the top of your mermaid cake using a cake spatula. It doesn’t need to be smooth; the lines going across look like ocean waves.
• Let the blue frosting set for a couple of minutes so it’s less sticky, then place your number made of parchment paper on top of the cake. Use a butter knife to score lightly around the edge of your number to create an outline and remove the paper. Then use light brown sugar to create a thin layer of ‘sand’ inside your number outline. You can also use crushed graham crackers instead of brown sugar if you prefer.
• Add swirls and dots of purple and dark blue frosting to your cake with your piping bags and tips. Press down lightly, squeeze out some frosting, then stop squeezing and pull your bag away. Start in alternating corners and create a pattern you like, or make it random.
• Keep filling in the edge of your cake with decorations until you’re happy with how it looks.
• Add your chocolate mermaid tails (and other seashells if you also have that second candy mold and made them, too).
• Then add your finishing touches of frosting and a touch of mermaid themed sprinkles on top of the cake.

Keyword Cake, mermaid

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