- 1 (18.25 ounce) box Betty Crocker® SuperMoist® cake mix (any flavor)
- 1 1/4 cups water
- 1/3 cup vegetable oil
- 3 eggs
- Tray or cardboard, 15×12 inches, covered
- 2 (16 ounce) tubs Betty Crocker® Rich and Creamy vanilla frosting
- Red, yellow and blue paste food colors
- 12 large marshmallows, cut in half crosswise
- Heat oven to 350 degrees F (325 degrees F for dark or nonstick pan.) Grease bottom and sides of 13×9-inch pan with shortening and lightly flour, or spray with baking spray with flour. Make cake mix as directed on box, using water, oil and eggs. Pour into pan.
- Bake as directed on box for 13×9-inch pan. Cool 10 minutes; remove from pan to cooling rack. Cool completely, about 1 hour.
- Using serrated knife, cut cake crosswise into thirds. Cut one of the thirds in half crosswise to make 2 squares. On tray, place cake pieces. Cover; freeze 1 hour or until firm.
- In small bowl for each color, tint 1 cup frosting red, 1 cup frosting yellow and 2/3 cup frosting blue with food colors. Leave remaining frosting white.
- Frost top and sides of 1 square cake with blue frosting. Frost 4 marshmallow halves with blue frosting; place in square design on cake. Frost remaining square cake and 4 marshmallow halves with white frosting; arrange marshmallows on top of cake. Frost 1 rectangular section of cake and 8 marshmallow halves with yellow frosting; arrange marshmallows on top of cake. Frost remaining section of cake and remaining marshmallows with red frosting; arrange marshmallows on top of cake. Store loosely covered at room temperature.