DIY Rainbow Unicorn Birthday Cake

Is there an extra special birthday coming up for someone in your household? If you have a kid who LOVES unicorns, they’re going to be amazed by this super easy rainbow unicorn birthday cake you make them. Birthday parties can be so expensive with the gifts, activities, and food. Then you add a cake on top of all the other expenses, and it can get a little overwhelming. If you’re trying to avoid paying a hundred dollars or more to have a custom cake made for your party and you’d like to try making something at home, you’ve come to the right place. 

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Even if you’re a total beginner like me, with a few layers of cake, a sprinkle covered ice cream cone, and lots of frosting, you can make the perfect Rainbow Unicorn Birthday Cake for a super fun unicorn themed birthday party. 

Table of Contents

How to make a rainbow unicorn birthday cake 

Gather up your ingredients and decide if you’re making a boxed cake mix or a recipe from scratch. You’ll also need to decide if you’re going to make a super inexpensive unicorn horn with an ice cream cone like I did, or if you’d rather purchase a unicorn cake topper set like this one. I highly recommend using quality food coloring if you want really vibrant colors in your cake and icing like this Wilton Food coloring set I used. Standard food coloring can become quite muted and pastel in color and the set I used has a built-in color guide so you know exactly how many drops of each one to use to get the desired effect. 


  • One box of white cake mix (or your favorite cake recipe)
  • Three eggs
  • Oil
  • Water
  • Butter
  • Vanilla
  • Milk
  • Wilton Food Coloring
  • Sugar Cones
  • Sprinkles


  • Mixing bowl
  • Electric Mixer
  • Spoons
  • Scissors
  • Spatula 
  • Cake board
  • Icing smoother
  • Measuring cups
  • Wax paper
  • Plastic wrap
  • Ziploc bags
  • Piping bag & tip
  • Round layer cake pan set

Preparation and Baking

It’s definitely helpful if you can bake your layered rainbow cakes in advance and put them in the freezer before you need to decorate. 

One box of cake mix perfectly portioned into this set of 4 layered cake pans from Wilton. I mixed all my ingredients together to form the cake batter, portioned out the batter into four different bowls, one scoop at a time to keep things even, and then added my food coloring to each bowl. To get the perfect color combination I used Wilton food coloring that comes with a color guide.

The key to creating magical unicorn cakes is to pick a color combination your unicorn lover will be happy with. Once the color is fully mixed in, line your cake pans with a circle of parchment paper and grease the sides of your pans. Pour in the cake batter, scraping the sides with a spatula to get all the batter into the pans.

Baking time will vary depending on your own oven and which cake mix you’re using. I baked my cakes for only 17 minutes at 350 Fahrenheit so they wouldn’t burn because they’re baking in such thin layers. 

Remove your cake from the oven and let it cool to room temperature in the pan. Once your cake is cool, use a long serrated bread knife to trim the top of the cake off while it is still in the pan if it is uneven. Spread out plastic wrap and carefully remove your cakes from their pans onto the plastic wrap once they’re cool. Wrap them up and put them in the freezer until they are solid; this will make them easier to decorate. 

Decorating A Rainbow Unicorn Cake

To get started decorating your easy rainbow unicorn cake, mix your buttercream frosting. If you’re tempted to use a can of icing for this step I have a word of caution for you… Canned icing is very sticky and the wrong thickness to use for a cake like this. It’s going to get super messy and the weight of it might break your cake. Don’t believe me? I did a test run of this rainbow unicorn cake with canned store bought icing and this is how it turned out.

My rainbow unicorn cake with store-bought icing cans

I made my buttercream frosting by mixing a brick of room temperature butter with 1 tbsp vanilla extract, up to ¼ cup of milk and 5 cups of powdered sugar together for 2 minutes until it’s smooth. 

I personally doubled this buttercream recipe just to make sure I had A LOT of it ready to go. The last thing I wanted was to run out and have to thaw out more butter. Separate out about 1 ½ cups of frosting into a bowl of pink food coloring and another 1 ½ cups of frosting into a second bowl of purple food coloring. Lastly, separate out about ½ a cup of frosting into a third bowl of black food coloring. Spoon the colored frosting into separate piping bags with your favorite decorating tips. I like using a star tip and no piping tip at all for the black details; I just cut a tiny hole in the tip of my piping bag.

For a total beginner like me, the freezer is your best friend. Freezing your cake will help prevent it from breaking. Freezing it again after the crumb coat will help give your cake a nice firm foundation on which you can put a second layer of buttercream frosting and smooth it out nicely without it pulling at your cake. 

To make your unicorn horn, grab a sugar cone (similar to a waffle cone but it has a smooth top edge) and coat it with a thin layer of icing. Roll the cone in gold sprinkles and set it aside. Use a knife or scissors to carefully cut two more sugar cones into similar sizes to use as your unicorn’s ears. (The ears help it look like an animal instead of just a cake with a pointy party hat.) Once you have the two ears cut out, put a bit of icing on them and outline them with the same black you’ll use to decorate the eyes. 

You could buy a unicorn cake topper on Amazon, but I found the nice quality ones to be quite expensive and I could buy a whole package of ice cream cones for about $3 at the grocery store for a similar look that’s entirely edible.

Add a layer of big sprinkles or round candy to the bottom of your cake. It can really help hide your mistakes if you’re a rookie like me. Place your unicorn ears and horn on the top of the cake and then add all your piping details like unicorn eyes on the front of the cake, and swirls of hair on the top and sides of the cake. Finish it off with some finer sprinkles on top for extra effect. 

Voila! Here is your DIY Rainbow Unicorn Birthday Cake!

Extra Notes

Sometimes on the day of your child’s birthday there is already a lot going on. So how do you have time to make a cake? For the first step, I baked my cake layers one day and put them in the freezer, the next day I iced the cake and put it in the fridge without the horn on top to save room. The day of the party, all you’ll have to do is bring it out of the fridge and put the horn on! Unicorn birthday cakes can seem like a lot of work, but breaking up the steps into different days can be super helpful.

I hope you’ve enjoyed this simple rainbow unicorn cake recipe! The unicorn trend is a really big deal for kids of all ages right now and super popular for birthday themes. Don’t get too caught up in making the details of your birthday cake perfect, your kid is going to be totally amazed you made them such a fun cake!

For more easy party inspiration, check out more articles from Mama’s Buzz!

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