Recipes & Cooking Desserts & Baking Cakes Rainbow Sheet Cake Be the first to rate & review! Guests are going to swoon after seeing the first slice of this rainbow cake. Our delicious, vibrant rainbow layer cake starts with a boxed mix and colored for an easy, yet super impressive dessert for birthdays or any celebration that calls for rainbows. By Sarah Brekke, MS Sarah Brekke, MS Sarah Brekke, a culinary expert with The Better Homes and Gardens Test Kitchen, is passionate about food and cooking. Her unique background as both a food scientist and a culinary contributor allows her to blend her passions for both educating readers and creating tasty content. Learn about BHG's Editorial Process Published on August 23, 2021 Rate PRINT Share Hands On Time: 45 mins Total Time: 2 hrs Servings: 12 Yield: 1 - 13x9 inch cake Jump to Nutrition Facts Ingredients 2 16.25 ounce packages white cake mix (plus ingredients required to prepare cake) Red, orange, yellow, green, blue, and purple gel food colors* 2 cup butter, softened 6 cup powdered sugar, sifted 2 teaspoon vanilla extract ½ teaspoon salt ¼ cup heavy cream Rainbow jimmies or other sprinkles Directions Preheat oven to 350°F. Cut 6 sheets of parchment paper to fit a 13x9-inch baking pan with extra paper overhanging on two sides for handles. Grease pan with nonstick spray and line with 1 sheet of parchment. In a medium bowl, prepare cake batter according to package directions. Divide batter evenly into 3 bowls (you should have about 1 1/3 cups batter per bowl). Tint one bowl red, one orange, and one yellow and stir until evenly mixed and vibrant. Pour red batter into prepared pan and bake about 10 minutes or until set. Remove pan from oven and cool on a wire rack for 10 minutes. Using parchment handles, remove cake layer from pan and cool completely (with parchment) on wire rack. Repeat with orange and yellow batter. Prepare second box of cake mix and this time tint portions green, blue, and purple. Bake as directed in step 3. Once all six cake layers are baked and cooled, use parchment to transfer to trays. Freeze cake layers for at least 30 minutes or until easy to handle. Meanwhile, wash and dry baking pan; set aside. To prepare frosting, in a large bowl beat butter on medium-high until creamy. Beat in powdered sugar on low speed, 1 cup at a time, until frosting is light and fluffy. Increase mixer to medium-high and beat 3 minutes more. Beat in vanilla extract and salt until combined. Add heavy cream and beat on medium-high 1 minute more. To assemble cake, remove parchment and place red layer in the bottom of the baking pan. Spread with about 1/2 cup frosting. Repeat with remaining cake layers and frosting. If desired, top cake with sprinkles. Rachel Marek Tips If desired, use purchased natural food colors (note: colors may not be quite as intense). Rate It Print Nutrition Facts (per serving) 1023 Calories 58g Fat 121g Carbs 7g Protein Show Full Nutrition Label Hide Full Nutrition Label Nutrition Facts Servings Per Recipe 12 Calories 1023 % Daily Value * Total Fat 58g 74% Saturated Fat 25g 125% Cholesterol 180mg 60% Sodium 896mg 39% Total Carbohydrate 121g 44% Total Sugars 89g Protein 7g 14% Calcium 99mg 8% Iron 1.8mg 10% Potassium 95mg 2% Fatty acids, total trans 3g Folate, total 55.9mcg Vitamin B-12 0.3mcg Vitamin B-6 0.1mg *The % Daily Value (DV) tells you how much a nutrient in a food serving contributes to a daily diet. 2,000 calories a day is used for general nutrition advice.