Instructions

White Cake Batter

1. Grease the 5 round cake pans and set them aside.
2. In a large mixing bowl, combine the all-purpose flour, baking powder, baking soda, and Kosher salt. Set aside.
3. Preheat the oven to 325 degrees F.
4. In a large mixing bowl, beat butter with a handheld electric mixer for about 30 seconds. Add the granulated white sugar and 1 teaspoon of pure vanilla extract. Beat until combined. Add the egg whites gradually, one at a time beat well after adding each one.
5. Add the flour mixture and buttermilk alternately to the butter mixture gradually. Mixing well after each addition. Add the butter evenly to each of the 5 baking pans.
6. Add drops of the gel food coloring to the 5 cake pans and gently stir to combine. (Alternately, you can mix the colors in separate bowls if you don't want to mix them in the cake pans.)
7. Bake for 17-20 minutes, rotating halfway during the baking time.
8. When the cake layers are done, cool on a wire rack for 5-10 minutes before removing from the pans on a wire rack to finish cooling completely. Make sure the cake layers are completely cool before frosting.

Buttercream Frosting

1. In a stand mixing bowl, add unsalted butter and beat for about 30 seconds.
2. Add vanilla and milk, and mix until combined.
3. Gradually add the confectioner's sugar, 1/2 cup at a time. Combine completely before each addition. Make sure the frosting is completely smooth before mixing gel food coloring in.
4. Divide the frosting in half. Half will be used for frosting the cake base and half will be further divided into colors for decorating the unicorn mane.
5. Divide the buttercream frosting into 3 equal bowls (or however many colors you wish to do). Add gel food coloring, and mix until the color is even. Add each bowl of frosting into piping bags with desired frosting tips. Set aside until ready to decorate.

Assembling the Unicorn Rainbow Cake

1. On a rotating cake stand, add a cardboard cake circle, add the first layer (red), add a little frosting to make a thin layer between the cake layers, add the 2nd layer (orange), and repeat with yellow, green, and purple cake layers. Use the remaining white frosting to frost the outside of the cake using an offset spatula and cake smoothing comb or bench/dough scraper. To get a smooth surface, you may need to refrigerate the cake before putting the final white layer on, depending on the temperature of the room you are working in.
2. Add the unicorn horn cake topper, the eyes, and the ears. (the unicorn cake topper that I use is linked in the recipe card below).
3. Now the fun part! Pipe the 3 frosting colors with tips to make the mane and forelock of the unicorn.
4. Add sprinkles to the piped flowers on the mane and forelock of the unicorn cake.
5. When the decoration is done, allow the cake to firm up in the refrigerator before serving.