A full tutorial shows you how to decorate a cake with rainbow frosting for a colorful gluten-free birthday cake!

This past December 30th I turned 28… :-O  Not accepting the fact that I have legally been deemed an adult for the past 10 years, I was adamant about making a rainbow birthday cake… Lisa Frank colors and all.  My friend Jenn and I have birthdays 3 days apart so oftentimes we celebrate together with all of our friends.  This year we went to my mom and her husband’s property with 17 of our closest friends and family and camped out by the San Marcos river.  Even though it dropped down to 29 degrees that night, we had a blast!

This cake reminds me of my all time favorite bakery’s vanilla cake from my hometown (which sadly does not make gluten free cakes).  It is dense and vanilla-y with loads of sugar frosting on top.  It easily fed all of us hungry campers, so I am sure you will be able to feed up to 24.  I have included instructions in the recipe below on how to prep your cake for the piping tutorial you will see in the video.  Decorating this cake is not nearly as difficult as it may seem, but it does take a bit of patience and a sprinkle of unicorn dust!  OK, not really, but man does it look like a unicorn needs to pop out of that cake.  Hope you enjoy!

(Shout out to Andrew Corrigan for making the video magic happen.)

Rainbow Birthday Cake | Gluten Free with L.B.
Rainbow Birthday Cake
Rainbow Birthday Cake | Gluten Free with L.B.
Rainbow Birthday Cake
Rainbow Birthday Cake | Gluten Free with L.B.
Rainbow Birthday Cake

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5 from 2 votes

Rainbow Birthday Cake

This rainbow decorated cake is a perfect addition to a birthday party. 
Rainbow Birthday Cake | An impressive rainbow frosted cake that is perfect for any anniversary, birthday or special occasion. A classic vanilla cake recipe is finished off with multi-color buttercream frosting!
Yield 24 servings
Prep 45 minutes
Cook 30 minutes
Total 4 hours 15 minutes
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Buttermilk White Cake

  • 2 c. butter melted
  • 4 c. sugar
  • 6 eggs
  • 2 t. vanilla extract
  • ½ t. almond extract
  • 2 ⅔ c. white rice flour
  • 1 ⅓ c. tapioca starch
  • 2 t. xanthan gum
  • Or 4 c. all purpose flour instead of the above 3 ingredients
  • 2 ½ t. baking powder
  • ½ t. salt
  • 1 ⅓ c. buttermilk

Buttercream Frosting (multiply recipe by 2 ½)

  • ½ c. butter
  • 6 c. powdered sugar
  • 1 egg white
  • 3-4 T. milk
  • 2 t. vanilla clear
  • ½ t. salt
  • Food coloring if desired (first batch (1x above recipe) all white for crumb coating, second batch (1.5x above recipe) for rainbow colors)

Piping Tutorial:

  • 4-6 piping bags
  • 4-6 couplers
  • 4-6 size 12 round piping tips


For the Buttermilk White Cake:

  • Preheat oven to 350 degrees.
  • If you have a bowl that fits at least 12 cups of ingredients, go ahead and make this batch as the ingredients are listed above for a 4-layered cake. However, if you do not, halve the ingredients and make two batches. (Half of ⅓ c. = 3 T.+1 t. )
  • Combine butter and sugar in a large bowl of a high speed mixer. Mix for 2 minutes on medium speed.
  • In a separate bowl, combine white rice flour, tapioca starch, xanthan gum, baking powder, and salt. Add in about 1 c. of dry ingredients to the butter/sugar bowl. Mix for 30 seconds.
  • Add eggs, one at a time, mixing well after each addition. Add in vanilla and almond extract.
  • Add remaining dry ingredients and buttermilk alternatively, starting and ending with dry ingredients. Beat for an additional minute to make batter light and fluffy.
  • Fill four well-greased 9-inch round cake pans with even amounts of cake batter. Bake for 25-30 minutes, or until a toothpick inserted in the center comes out clean.
  • Let cool for 5-10 minutes before flipping out.

For the Buttercream Frosting:

  • Cream butter, 2 c. powdered sugar and egg white in the bowl of an electric mixer.
  • Alternatively add 1 c. sugar and 1 T. milk until all sugar is added.
  • Add in vanilla, salt and food coloring, if desired.

For the Cake Prep:

  • Prep your cake for the rainbow icing instructional video by using the first batch of frosting. Place the first layer down, ice the top with a ¼- ½ inch layer of frosting and repeat with the remaining 3 layers.
  • Trim any uneven edges around the cake and finish the cake prep by applying the remainder of the frosting on the sides of the cake.
Last step! If you make this, please leave a review letting us know how it was!

Tap stars to rate!

5 from 2 votes


Calories: 724kcal, Carbohydrates: 131g, Protein: 3g, Fat: 21g, Saturated Fat: 13g, Cholesterol: 95mg, Sodium: 227mg, Potassium: 62mg, Sugar: 97g, Vitamin A: 695IU, Calcium: 30mg, Iron: 0.5mg

Nutrition information is automatically calculated, so should only be used as an approximation.

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