Making a rainbow unicorn cake isn’t as hard as it looks. While this popular cake can be a lot of work, we’re going to take advantage of some shortcuts to help ourselves out. Use this recipe, tutorial, and tips to make a delicious cake for a special occasion.

Using boxed cake mixes and a unicorn cake topper kit that includes the horn and eyelashes takes away some of the labor-intensive work making this an easy rainbow unicorn cake recipe.

Don’t cheat on the buttercream though. There’s nothing like homemade buttercream frosting for both taste and decorating results.

Kids will love both the unicorn theme and the special rainbow surprise after the cake is sliced. You can make a rainbow unicorn birthday cake or enjoy it as a sweet treat anytime!

completed rainbow unicorn cake with two pieces sliced out and resting on plates so you can see the rainbow layers

Rainbow Unicorn Cake Ingredients
How to Make a Unicorn Cake
Unicorn Rainbow Cake Recipe Notes
Cake Decorating FAQs

Rainbow Unicorn Cake Ingredients

2 Boxed White Cake Mixes

Prepared Medium Consistency Vanilla Buttercream Frosting (for decorating)

Prepared Thin Consistency Vanilla Buttercream Frosting (for icing) – See notes on Wilton Vanilla Buttercream recipe above on thinning your medium consistency recipe

Gel food colors

Unicorn Cake Topper Kit

How to Make a Unicorn Cake

Prepare cake mix according to box instructions. Be sure to separate the eggs and use only egg whites so the batter will have strong colors giving you a nice rainbow effect.

Evenly separate the cake mix into four bowls and add electric gel colors. 2-3 drops of different color food coloring per bowl should be enough.

4 pans and four bowls of cake batter with food coloring in each one of them ready to be mixed

Lightly grease cake pans and pour batter into prepared pans.

Bake cakes according to box instructions checking at the 15-minute mark.

Remove from oven and allow to cool at room temperature until the cakes are cool enough to be wrapped in plastic wrap and placed in the freezer.

Make your buttercream with an electric mixer while the cakes cool in the freezer.

Crumb coat the cake with a thin layer of white frosting making sure to put the buttercream in between each layer as you build a cake. The easiest way to do this is directly on the base of a cake stand or on a disposable cake board.

Prepare your colored frosting and put it into piping bags with star tips. A medium-stiff consistency icing is going to be required to create the roses on top of the unicorn’s head.

Remove the unicorn horn cake topper from its package and center it at the top of the cake.

After placing the unicorn horn topper on top of the cake select your eyelashes and placing them as symmetrical as possible.

crumb coated unicorn cake with topper and eyelashes added. yellow, red, and teal icings are in frosting bags in the foreground

Use different shape/sizes star tips to create the roses and border as you like. See photo below.

Unicorn Rainbow Cake Recipe Notes

Because these are 1-inch cake layers they may cook faster than your box tells you. Begin to check them at the 15-minute mark.
Cakes are done when you stick a toothpick in it and it comes out clean.
While freezing the cakes is not necessary it is strongly encouraged as it will make the icing of the cake easier when it’s time to assemble.
If you are in a rush chill the cakes in the fridge for at least two hours before attempting to assemble the cakes or else the cakes can come apart when you are icing them.
While using a coupler is not necessary for this particular activity it will be helpful to change the tips out.
A medium-stiff consistency icing is going to be required to create the roses on top of the unicorn’s head.
Make sure you hold your piping bag at a 45° angle. Apply even pressure when squeezing out the icing. Stop squeezing and then pull the tip away.

Cake Decorating FAQs

What do I do if I don’t have a piping bag?

While I strongly encourage you to purchase piping bags, you may use a small sandwich bag but it will require you to have a piping tip.

Can I use plastic tips?

Yes you can use the plastic decorating tips. However you will not be able to change out the tips while you’re decorating.

Why do we use couplers when decorating?

The couplers make it easy for you to change the piping tip while still using the same color.

What’s the best way to clean the piping tips?

Boil them in hot water and allow them to air dry.

How do I transfer the cake to a cake stand?

Stack the layers of cake onto a cake board and decorate it completely. Then, transfer the cake, board and all, to the cake stand.

Rainbow Unicorn Cake Recipe

Yield: 1 Cake

Prep Time: 25 minutes

Cook Time: 15 minutes

Additional Time: 2 hours

Total Time: 2 hours 40 minutes

Making a rainbow unicorn cake isn't as hard as it looks. Use this recipe, tutorial, and tips to make a magical cake for a special occasion.

Ingredients

2 White Boxed cake mix, prepared according to box instructions
Gel food coloring
Buttercream icing

Instructions

Prepare cake mix according to box instructions.
Separate the cake mix into four bowls using electric gel colors 1 to 2 drops of coloring will be enough for a favorite cake color.
Lightly grease cake pans.
Import prepared batter into pans.
Bake according to box instructions. (Because these are 1-inch cake layers they may cook faster than your box tells you. Begin to check them at the 15-minute mark. Cakes are done when you stick a toothpick in it and it comes out clean.
Remove the cakes from the oven and allow them to cool at room temperature until the cakes can be wrapped in plastic wrap and placed in the freezer. (While freezing the cakes is not necessary it is strongly encouraged as it will make the icing of the cake easier when it’s time to assemble. If you are in a rush chill the cakes in the fridge for at least two hours before attempting to assemble the cakes or else the cakes can come apart when you are icing them.)
Make buttercream icing.
Crumb coat the cake with a thin layer of vanilla buttercream making sure to put the buttercream in between each layer as you build the cake.
Allow the cake time to rest before moving on to the next step. (Buttercream icing will crust over meaning when you touch it with your finger after about 15 minutes the Icing is no longer wet.)
Prepare your colored frosting and put it into piping bags with star tips. (While using a coupler is not necessary for this particular activity it will be helpful to change the tips out.) A medium-stiff consistency icing is going to be required to create the roses on top of the unicorns head
Remove the unicorn horn cake topper from its package and center it at the top of the cake.
After placing the unicorn horn topper on top of the cake select your eyelashes and placing them as symmetrical as possible.
Using a star tip, create roses on top of the cake and around the base.