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Rainbow Layer Cake

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Ingredients
  

For the Cake:

  • Baking spray
  • 2 15.25-ounce packages Duncan Hines Classic White Cake Mix
  • 1-1/2 cups water
  • 6 eggs
  • 2/3 cup vegetable oil
  • 2 tsp. vanilla extract
  • Red, orange, yellow, green, blue and purple food coloring

For the Buttercream Frosting:

  • 3 cups unsalted butter, softened
  • 1/4 cup heavy whipping cream
  • 4 tsp. vanilla extract
  • 1 tsp. salt
  • 1 32-ounce bag confectioners' sugar

Instructions
 

To prepare the cake:

  • Pre-heat oven to 350°F.
  • Spray three 9-inch round cake pans with baking spray.
  • In a large bowl, with an electric mixer at low speed, blend cake mix, water, eggs, oil and vanilla until moistened; continue to beat, at medium speed, for 2 additional minutes.
  • Divide batter evenly into 6 bowls, about 1 1/2 cups each; add 1/2 teaspoon red food coloring to one bowl, 1/4 teaspoon yellow to another and 1/4 teaspoon orange to a third bowl of batter; stir each until blended.
  • Pour each into separate pans; place in pre-heated oven and bake 14 to 16 minutes, until toothpick comes out clean; cool 10 minutes; remove from pans to cooling racks and cool completely.
  • Meanwhile, add 1/2 teaspoon blue food coloring to one of the remaining bowls of batter, 1/2 teaspoon green to another and 1/2 teaspoon purple to the final bowl; stir until blended. refrigerate until ready to bake.
  • Wash, dry and spray cake pans with baking spray; pour each remaining color into separate pans and bake 14 to 16 minutes, until toothpick comes out clean; cool 10 minutes; remove from pans to cooling racks and cool completely.

To prepare the buttercream frosting:

  • In a large bowl, with an electric mixer, on low speed, beat butter, heavy cream, vanilla and salt until blended; about 1 minute.
  • Slowly beat in confectioner's sugar until smooth.
  • Increase speed to medium and beat until light and fluffy; about 3 to 5 minutes.

To assemble the rainbow layer cake:

  • Trim rounded tops off cakes, to level, if necessary.
  • Place purple cake layer on cardboard round; spread with about 1/2 cup frosting; top with blue cake layer and press lightly to adhere; repeat with green, yellow, orange and red cake layers.
  • Spread a light coating of frosting all over sides of cake; refrigerate 15 minutes.
  • Remove from refrigerator and frost with remaining frosting.
  • Transfer cake to a serving plate.