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A tall cake on a white stand features green and white stripes, chocolate drip topping, and decorative whipped cream swirls with chocolate cookies. It sits on a marble surface against a plain background.
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Thin Mint Party Cake

This chocolate cake, complete with a mint Swiss meringue buttercream and an incredible Chocolate Ganache is seriously a dream come true. And the best part? It’s inspired by Girl Scout Cookies! With mint and chocolate mixed together in the perfect way, you’ll be raving about this cake long past St. Patrick’s Day.
Author: Ashley Byma

Ingredients

  • Dark Chocolate Cake
  • 1 cup heaping regular cocoa powder
  • ¼ cup heaping dark cocoa powder
  • 2 ½ cups all-purpose flour
  • 2 ½ teaspoons baking soda
  • 1 ¼ teaspoons baking powder
  • 1 ¼ teaspoons salt
  • 1 ½ cups white sugar
  • 1 cup dark brown sugar packed
  • 5 large eggs + 1 egg yolk
  • 1 ¼ cups warm water
  • 1 ¼ cups buttermilk
  • ½ cup + 2 tablespoons vegetable oil
  • 2 teaspoons vanilla extract
  • Mint Chocolate Ganache Filling
  • 1 ½ cup bittersweet chocolate chips
  • ½ cup heavy whipping cream
  • ¾ teaspoon mint extract can substitute with peppermint if extract does not contain water
  • Optional: crumbled Thin Mint cookies for adding between cake layers & topping
  • Mint Swiss Meringue Buttercream
  • 1 batch of SMBC recipe and directions found here
  • ¾ teaspoon peppermint extract
  • ¾ teaspoon mint extract can substitute with peppermint

Instructions

Dark Chocolate Cake:

  • Preheat oven to 350° F. Spray three 6-inch cake pans with cooking spray, and line the bottoms with parchment paper. *Note that the recipe for this batter typically makes three 8-inch layers; you can make 2 extra 6-inch layers or cupcakes with the remaining batter.
  • In the bowl of a stand mixer fitted with a whisk attachment, add all dry ingredients (cocoa powders, flour, baking soda, baking powder, salt, white sugar, brown sugar) and mix on low-medium speed until combined.
  • Add the eggs+ yolk, water, buttermilk, oil and vanilla and mix on low-medium until fully incorporated and there are no big lumps. Do not overmix.
  • Divide batter evenly into three 6-inch cake pans and bake for approximately 25 minutes or until the middle is mostly set. Use a toothpick to test; if it comes out with a few crumbs then it is ready.
  • Remove from oven and let cool. Transfer to countertop covered with parchment paper by running a knife around the cake edges, then turning the cake pan upside down to release the cake. Once completely cool, you can wrap these in saran wrap and place in a gallon size freezer bag; you can freeze the cake layers for about 2 months. When ready to fill the cake, use frozen cake layers to prevent the cake from crumbling while decorating.
  • Mint Chocolate Ganache Filling
  • Add chocolate to mixing bowl and set aside.
  • Add heavy cream to a saucepan, and heat on medium until it just starts to boil around the edges and center (be careful as this can boil over very quickly).
  • Remove cream from heat and slowly pour over the chocolate. Let rest for about 5 minutes, then use a whisk to stir the chocolate/cream mixture until fully incorporated and smooth.
  • Add mint extract and stir until fully incorporated. If using peppermint extract, be sure there is no water in the ingredient listing as this will cause the chocolate to seize (oil is fine).
  • Let sit at room temperature, or refrigerate, until it is the same consistency as peanut butter. This makes it easy to fill the cake layers.

Assembly:

  • If the cake layers do not bake evenly, you can use a bread knife to trim the top off and make it flat which is easier for decorating. You will need to let the cake layers thaw just a bit before trimming.
  • Start with the frozen chocolate cake layers, and place one layer on a cake board. You can use a spoonful of buttercream as “glue” between the cake layer and cake board if you like.
  • Spread an even layer of mint buttercream over the top of the 1st cake layer. Pipe a circle of buttercream around the perimeter of the cake layer to create a barrier before adding the chocolate ganache (this will prevent the ganache from spilling over the edges of the cake).
  • Spread an even layer of chocolate ganache over the mint buttercream and topped with crumbled Thin Mints.
  • Repeat with remaining cake layers and frost the outside with the swiss meringue buttercream.