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Rainbow Petal Cake

Soft vanilla cake layers with creamy vanilla buttercream.

Course Dessert
Cuisine American
Keyword Buttercream, Cake Decorating, Cake Recipe, vanilla cake
Prep Time 1 hour
Cook Time 45 minutes
Cooling/Decorating Time 2 hours 30 minutes
Total Time 4 hours 15 minutes
Author Katie

Ingredients

Vanilla Cake

  • 1 cup (or 2 sticks) unsalted butter, room temperature
  • 1/2 cup vegetable oil
  • 2 cups granulated sugar
  • 6 large whole eggs
  • 2 large egg yolks
  • 3 cups cake flour (or 2 ¾ cup ap flour & ¼ cup cornstarch)
  • 2 teaspoons baking powder
  • 1 teaspoon salt
  • 1 cup buttermilk
  • 2 teaspoons vanilla extract

Vanilla Buttercream

  • 2 cups (or 4 sticks) unsalted butter, room temperature
  • 1 teaspoon salt
  • 2 teaspoons vanilla extract
  • 7 1/2 cups powdered sugar, sifted
  • 2-3 Tablespoons heavy cream
  • Deep pink, peach, yellow, green, sky blue, brite purple gel food coloring

Instructions

Vanilla Cake

  1. Preheat the oven to 350 °F. Spray three 6-inch round cake pans with non-stick spray, line the bottom of each pan with parchment paper and spray again. Set aside.

  2. In a medium-size bowl, whisk and stir together the flour, baking powder, and salt. Set aside.

  3. In the stand mixer bowl fitted with a paddle attachment, beat the butter, oil, and sugar on medium-high for 5 minutes.

  4. Add the eggs, one at a time to the stand mixer bowl and beat on medium until well incorporated.

  5. Turn the mixer on low and add the flour mixture to the butter mixture until fully incorporated.

  6. Pour in the buttermilk and vanilla extract. Mix on medium for another 30 seconds and scrape down the sides of the bowl.

  7. Evenly distribute the cake batter among the three cake pans and bake for about 30-35 minutes or until a toothpick inserted into the center of each cake comes out clean or with just a few moist crumbs.

  8. Remove cakes from the oven and let cool in pans for 10 minutes before inverting onto cooling racks to cool completely. Wrap cakes in plastic wrap and place them into the freezer to chill for 30 minutes to 1 hour.

Vanilla Buttercream

  1. In the stand mixer bowl fitted with the paddle attachment, beat the butter until light and fluffy, about 2 minutes.

  2. Turn the mixer to low and add the salt and vanilla.

  3. Next, gradually add powdered sugar, followed by the cream. Mix on medium-high speed for about 5 minutes, until light and fluffy. Scrape down the sides of the bowl.

  4. Before using, turn the mixer on low and mix for 2 minutes to push out any air bubbles or use a rubber spatula to push out the air bubbles. (You may need to repeat this step when frosting the outside of the cake).

  5. Divide buttercream into six bowls (reserve some white buttercream for later, if necessary to refill another color).

  6. Then color with deep pink, Georgia peach, lemon yellow, leaf green, sky blue, and brite purple. Place the colored buttercreams into individual piping bags, set aside.

Assemble

  1. Remove the cake layers from the freezer and unwrap the cake layers. Next, use a serrated knife to cut off the dome of the cakes to make the layers flat and even.

  2. Add a small amount of buttercream onto the center of the cake board. Layer one cake layer, cut side up onto the cake board. Pipe a ring of pink buttercream in the center of the cake, followed by rings of peach, yellow, green, blue, and purple buttercream on the outside. Use an offset spatula to smooth the buttercream layer.

  3. Place another cake layer cut side down over the top. Repeat the process for another layer — Crumb coat with buttercream and freeze for 30 minutes.

  4. Starting from the bottom of the cake, pipe a single dot about 1-inch of one color buttercream. Then pipe another color dot above the previous dot and continue to pipe dots in a straight line up the cake alternating the buttercream colors.

  5. Use an offset spatula to press and pull the dot towards the side of the cake. Repeat the process until you have one column completed. (Scrape off the colored buttercream into a bowl to keep the spatula clean in between each color).

  6. To start a new column, pipe the next dot overlapping the previous pulled dot. Alternate the colors to create a petal effect. Repeat the process all over the whole cake.

  7. Serve at room temperature and enjoy!

Recipe Notes

  • Read through all the ingredients and instructions so you can get a better idea of how much time and what you need to make this cake.
  • A single batch of this cake recipe makes three, 6-inch round cake layers or two 8-inch round cake layers. Double the cake recipe to make enough cake batter for three, 8-inch cake layers.
  • In this cake recipe, you need ½ cup buttermilk; if you don't have any buttermilk on hand, you can easily use ½ cup whole milk mixed with 2 teaspoon lemon juice or white vinegar to make your own. 
  • To make cake flour at home, mix 2 ¾ cups all-purpose flour and ¼ cup cornstarch. Sift or whisk together to get rid of any lumps. 
  • Be careful not to overmix this cake batter, or else the cake will come out dense. Mix until all ingredients are well incorporated.
  • You can bake the cake layers ahead of time. Wrap the cake layers in plastic wrap and freeze up to one month. 
  • Food coloring gets darker over time, so it's best to add the food coloring gradually. 
  • You can make the vanilla buttercream a day or two ahead and refrigerate them overnight. Then take them out to come back to room temperature. Make sure the buttercream is at room temperature before re-whipping. 
  • Serve at room temperature and enjoy!