Pastel Rainbow Cake

5 from 3 votes

This easy rainbow cake recipe is made with pastel colors! Make a pastel rainbow cake for a birthday or turn it into a unicorn cake! The cake is decorated with watercolor frosting and sprinkles

Prep Time1

Cook Time30

Decorating1

Total Time2 30

Course: Dessert

Cuisine: American

Servings: servings

Calories: 615kcal

Author: Dorothy Kern

Cost: $13

Equipment

Pastel Food Coloring
Pastry Bag
1M Tip
4-6 of the same cake pan

Ingredients

For the Cake:

1/2 teaspoon salt
3 teaspoons baking powder
2 1/2 cups all-purpose flour
1 cup unsalted butter, melted
1 1/2 cups granulated sugar
4 large eggs
1 tablespoon vanilla extract
1 1/4 cups buttermilk
Pastel food coloring

For the frosting:

1 1/2 cups unsalted butter, softened
6 cups powdered sugar
1/2 teaspoon salt
1 tablespoon vanilla extract
3-4 tablespoons heavy whipping cream
Sprinkles optional

Instructions

For the cake:

Preheat oven to 350°F. Grease and flour 4-6 (8-inch round) cake pan(s). (Pictured: 4 pans)
Whisk salt, baking powder, and flour in a medium sized bowl. Set aside.
Using a hand mixer, cream sugar into melted butter until smooth. Beat in eggs, one at a time, then mix in vanilla extract.
Add dry ingredients alternately with the buttermilk, starting and ending with the flour, mixing gently between each addition. Mix until just combined. Be sure to scrape the sides of the bowl.
Divide batter into as many equal parts as you have pans (i.e. if you want 4 layers, separate it into 4 bowls). Add a few drops of pastel food coloring to each bowl. Stir to color, then pour into prepared pans.
Bake for 20-30 minutes, or until a toothpick comes out clean. The cake will bake faster than regular thickness layers would bake. If you're making more than 4 layers it might take less time. Cool the cakes completely before frosting.

For the frosting:

Beat butter until smooth with a hand or a stand mixer. Note: if you’re using a hand mixer be sure to use a very large bowl to avoid wearing the powdered sugar.
Add powdered sugar, one cup at a time, and beat on medium speed until crumbly. Mix in salt and vanilla.
Add 1 tablespoon of heavy whipping cream at a time, mixing between each addition, until the frosting is smooth and the desirable consistency.
Divide and color the frosting as desired. (Pictured: 3 colors: pink, purple and white)

Decoration:

Place the bottom cake layer on cake plate. Frost with a layer of frosting. Add the layers, frosting in between each, until the cake is assembled.
Make a crumb coat of frosting. This is a very, very thin layer of frosting that you frost the entire cake with. Chill the crumb coated cake until set.
Frost the cake as desired with remaining frosting. Details below:
For the watercolor look: drop dollups of different color frostings all over the cake like polka dots. Use an offset spatula to spread them and swirl. Be careful not to mix the frosting colors too much.
To make a swirled frosting for the top: lay a sheet of plastic wrap on the counter. Place any remaing frosting in three lines and wrap the palstic wrap up. Cut off one end and add it to a pastry bag set with a 1M tip. Top the cake with rosettes and sprinkles.
Chill to set. Store covered in the refrigerator for up to 2 days.

Video

Notes

Use a box mix if you prefer, and even canned icing.
You can do this same recipe to make ANY color layers.
It's best if you use the SAME brand cake pan for all the layers. Different brands/units might be different sizes even if they say they're all 8-inches.
Fill the cake with other flavors, like lemon curd or chocolate frosting.
For a visual on how to do the swirl frosting, check out my Unicorn Cupcakes tutorial.

Nutrition