1 box white cake mix
1 1/4 cups buttermilk
1/3 cup vegetable oil
1 tablespoon unsweetened baking cocoa
2 teaspoons royal blue paste food color
1 toothpickful violet paste food color
1 jar (7 oz) marshmallow creme
1 cup butter or margarine, softened
2 1/2 cups powdered sugar
1/8 teaspoon salt
- Heat oven to 325°F. Grease and lightly flour bottoms and sides of three 8-inch round cake pans, or spray with baking spray with flour.
- In large bowl, beat cake ingredients with electric mixer on low speed about 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally.
- Divide batter evenly among pans. Bake 22 to 27 minutes or until top springs back when lightly touched in center. Cool 15 minutes. Remove from pans; cool completely.
- Spoon marshmallow creme into large microwavable bowl; microwave uncovered on High 15 to 20 seconds to soften. Add butter. Beat with electric mixer on medium speed until smooth. Beat in powdered sugar and salt until smooth.
- If necessary, trim rounded tops of 2 cake layers to flatten before assembling. Place 1 cake layer, top side down, on serving plate; spread with about 1/3 cup frosting. Top with second layer, top side down; spread with about 1/3 cup frosting. Top with untrimmed cake layer, top side up. Frost side and top of cake with remaining frosting. Store loosely covered.