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image of a slice of mermaid layer cake sitting on a plate with the rest of the cake in the background

Mermaid Cake with Vanilla Buttercream

This mermaid cake is delicious and easy to make because it uses a box cake mix. Just don’t forget the sprinkles!
Course Dessert
Cuisine American
Prep Time 20 minutes
Cook Time 30 minutes
Cooling Time 3 hours
Total Time 3 hours 50 minutes
Servings 8
Author Kelsie



  • 1 15.25-ounce box white cake mix
  • 1 3-ounce box vanilla or white chocolate pudding
  • 1 cup sour cream
  • 3/4 cup vegetable oil
  • 1/2 cup whole milk
  • 4 large egg whites
  • blue and green gel food coloring


  • 1 cup unsalted butter at room temperature
  • 4 1/2 to 5 cups powdered sugar
  • 2 to 5 tablespoons milk or heavy cream
  • 1 tablespoon clear vanilla extract can substitute regular
  • 1/4 teaspoon salt
  • Purple gel food coloring
  • Sprinkles



  1. Preheat the oven to 350 degrees. Spray 2 8-inch round cake pans with cooking spray. Line the bottoms of the pans with parchment, then spray the pans again and lightly dust with flour. Set aside.
  2. Combine the cake mix, pudding mix, sour cream, vegetable oil, milk, and egg whites in a large mixing bowl. Beat with an electric mixer set to medium until smooth.
  3. Divide the batter evenly between three mixing bowls (each bowl will have about 1 2/3 cups batter). Stir blue food coloring into one and green into another. Leave one bowl white.
  4. Drop a large spoonful (about 3 to 4 tablespoons) of blue batter into one of the pans. Top with a large spoonful of green, then a large spoonful of white. Continue going in that pattern until you’ve used about half of each color. Jiggle the pan now and then so the batter evens out. Repeat with the second pan. Once you’ve used all the batter, gently shake them so the batter goes all the way to the edge of the pans.
  5. Bake 30 to 34 minutes, until a toothpick inserted into the center of the pans comes out clean. Cool in pans for 10 minutes, then remove cakes to a wire rack to cool completely before frosting.


  1. Place the butter in the bowl of a stand mixer fitted with the paddle attachment and beat until very smooth. Add 4 1/2 cups of the powdered sugar, 2 tablespoons of the milk or cream, and the vanilla and salt. Mix on low until well combined then add food coloring to achieve desired color. Turn mixer to high for 3 to 4 minutes, beating until frosting is very light and fluffy. Add additional powdered sugar if frosting is too thin and additional milk or cream if it is too thick.


  1. If your cakes have domed, use a long serrated knife to even them out. Place one layer on a cake stand or cardboard cake circle and spread frosting in an even layer over the top. Top with second cake layer and cover cake with a thin layer of frosting. Refrigerate until frosting is set (this is your crumb coat and will prevent crumbs from getting into your final layer of frosting). Use remaining frosting to frost and decorate as desired. Serve and enjoy.