6 Layer Rainbow Cake Recipe with Easy Buttercream Frosting
This homemade dessert recipe for a 6 Layer Rainbow Cake Recipe is easier than it looks thanks to boxed cake mix. Nonetheless, the beautiful and vibrant colored layers really make a statement especially when it’s topped off with a delicious homemade buttercream frosting!
Ingredients
For Cake:
- 2 boxes white cake mix
- 6 eggs
- 2/3 cup canola oil
- 2.5 cup water
- Wilton Gel Food Coloring
Ingredients for Buttercream Frosting
- 1 cup unsalted butter 2 sticks, room temperature
- 4 tbsp. milk
- 4 tsp. clear vanilla extract
- 4 cups powdered sugar
Instructions
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The night before preparing the cakes and assembling, using a piece of wax paper and a pencil trace the outline of the bottom of your cake pan. You can use the disposable cake pans for tracing but the disposables I bought had a curved bottom so I used my own 9" cake pan which had a uniform edge. From your template, you're going to make 14 circles made of wax paper for this project.
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Cut out the circular wax paper pieces.
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Mix all buttercream frosting ingredients together until desired consistency. If your frosting ends up too thick, continue adding milk 1 tablespoon at a time until the mixture is what you're looking for.
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Spread a thin layer of buttercream frosting on a wax paper cake pan template. Cover with a new circle and repeat, stacking your layers of buttercream frosting, until you have one wax circle left to place on top. You will have one extra layer of buttercream frosting in case any of your layers fall apart during assembly.
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Carefully place your dividing layers of buttercream in the freezer until ready to assemble your cake the following day.
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Refrigerate remainder of buttercream frosting until ready to frost cake.
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Set aside remaining wax circles until the following day when you'll coat with cooking spray and use these to line the bottom of your disposable baking pans. Lightly spray additional cooking spray to sides of cake pans.
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The next day, preheat your oven according to cake mix box directions - usually 350 degrees.
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Mix cake mix, eggs, oil, and water together until blended (about 2 minutes).
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Evenly divide cake batter in mixing bowls.
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Add gel food coloring to each individual bowl, adding a small amount at a time until you achieve your desired colors.
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Pour batter into baking pans and place all pans in oven to cook for approximately 8-12 minutes. Make sure to keep an eye on your cakes during this stage as cooking times will vary and these cakes are very thin.
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Once cakes are done, allow to cool in pan for 10 minutes before inverting pans on baking racks to finish cooling.
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When the cakes are cooled, if needed using a serrated knife cut tops to make flat edges for the layers.
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On a cake stand or foil covered surface, place your bottom layer of cake followed by a frozen layer of buttercream frosting. Continue alternating cake and frosting until all layers are assembled. Since this cake is so heavy, I cut three straws to the height of the cake and stuck them into the cake to provide stability.
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Icing a cake this size can be really tricky. I used a plastic spatula to plop some frosting on top of the cake, then I used a metal offset spatula to smooth it all over creating a thin layer to seal in the crumbs. Then repeat using more icing and spread an even layer of buttercream frosting on your cake. You can use the edge of your metal spatula to smooth things out. If you're looking for an even smoother, more finished look I've heard a bench scraper would really make a difference and get the job done perfectly.