Ingredients:

  • 2 cups all-purpose flour
  • ¾ cup unsweetened cocoa powder
  • 1 ½ tsp baking soda
  • ½ tsp salt
  • ½ cup unsalted butter, softened
  • 1 cup granulated sugar
  • ½ cup brown sugar, packed
  • 1 large egg, room temperature
  • 1 tbsp vanilla extract
  • 1 cup buttermilk, room temperature
  • ½ cup hot water or hot coffee
  • ½ cup unsalted butter, softened (for filling)
  • ½ cup vegetable shortening
  • 7 oz marshmallow fluff/creme
  • 1 ½ cups powdered sugar
  • 1 tsp vanilla extract (for filling)

Instructions:

  1. Preheat your oven to 350°F (180°C). Grease two 8-inch or 9-inch round cake pans and line the bottoms with parchment paper for a clean release.
  2. In a medium bowl, whisk together the all-purpose flour, baking soda, and salt until combined.
  3. Bloom the cocoa by whisking the unsweetened cocoa powder into the hot water or coffee in a small bowl until smooth. Set aside to cool slightly.
  4. In a stand mixer or large bowl, beat 1/2 cup softened butter with the granulated sugar and brown sugar for about 3 minutes until pale and aerated.
  5. Add the egg and 1 tablespoon of vanilla extract to the butter mixture, beating until fully incorporated.
  6. Alternately add the dry flour mixture and the buttermilk to the batter, beginning and ending with the dry ingredients. Stir in the bloomed cocoa mixture until the batter is smooth.
  7. Divide the batter evenly between the prepared pans. Bake for 25 minutes, or until a toothpick inserted into the center comes out clean.
  8. Allow the cakes to cool in the pans for 10 minutes before transferring them to wire cooling racks to cool completely.
  9. Prepare the filling by beating the remaining 1/2 cup butter and vegetable shortening until smooth. Add the marshmallow fluff, powdered sugar, and 1 teaspoon of vanilla, whipping until the mixture is light and puffy.
  10. To assemble, place one cake layer flat-side up on a serving plate. Spread the marshmallow filling thickly over the layer, then top with the second cake layer.