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Mermaid Fin Cake

Over unicorns? Try this blue, teal and purple marble cake decorated to look like a beautiful mermaid fin!


  • 1 ½ cups unsalted butter, room temperature
  • 3 cups sugar
  • 9 eggs, room temperature
  • 1 ½ tsp vanilla extract
  • 4 ½ cups all-purpose flour
  • 1 ½ tsp baking soda
  • 1 ½ tsp salt
  • 1 ¾ cups buttermilk
  • teal, blue and purple food colouring
  • Buttercream:
  • 3 cups unsalted butter, room temperature
  • 1 ½ tsp vanilla extract
  • 7 cups confectioner’s sugar
  • ½ cup white candy melts
  • 3 green candy melts
  • 2 yellow candy melts
  • 1 tsp vodka, or any clear food colouring
  • purple luster dust
  • gold luster dust


  1. Bake the cake: Beat the butter and sugar with an electric mixer until pale and fluffy. Add the vanilla extract and eggs one a time, mixing with each addition. In a separate bowl, combine the flour, baking soda and salt. Add this to the batter in 2 additions, alternating with the sour cream. Divide the batter between 3 bowls. Dye them teal, blue and purple. Pour the 3 different shades between 3 greased and floured 8-inch round cake pans, then swirl with a knife. Bake at 350F for 30 minutes, or until a skewer inserted into the cakes comes out clean. Cool in the pans for 10 minutes, then transfer to a wire rack and cool completely. The cakes may deflate slightly after coming out of the oven, but don’t worry!
  2. Make the buttercream: Beat the butter with an electric mixer until pale and fluffy. Add the vanilla extract and beat until combined. Add the confectioner’s sugar one cup at a time, then beat for 3-5 minutes, until fluffy.
  3. Assembly: Slice the tops and bottoms off the cakes to remove any excess browning. Stack the cakes, spreading some buttercream between each layer. Use a serrated knife to carve the cake into a pointed, dome-like shape. Don’t worry about cutting off so much cake – you can use this cake to make cake pops! Coat the entire cake in the buttercream. Crumbs may get caught up in the buttercream, but this will prevent them from getting stuck in the top layer of buttercream. Divide the remaining buttercream into 3 bowls and dye them teal, blue and purple. Place them into piping bags fitted with large, round piping tips. Working from the top, pipe rows of dollops of buttercream. To create the scallop pattern, pipe one row of dollops, then use a rounded spatula to smush the center of the dollop and drag it downwards. Wipe the spatula between each dollop, then continue to the next row. Cover the entire cake in buttercream scallops. To make the fin, combine the white, green and yellow candy melts in a microwave-safe bowl and microwave at 30-second intervals until fully melted. Draw a fin onto a sheet of parchment paper, making sure to extend the fin downwards, creating an extension that will stick into the cake. Flip over onto a baking sheet, so that the side with the ink is facing down. Spread the candy melts onto the parchment paper, using the drawing as a template. Transfer the baking sheet to the freezer for the candy melts to set, about 20 minutes. Dip a clean paintbrush into vodka, or any clear food coloring, then dip into gold and purple luster dust. Paint this onto the chocolate fin, to create a beautiful sheen. Then stick the fin into the top of the cake and enjoy!