Velvet Cocoa Cake with Instant Buttercream
To make decorative icing lines, gently drag the rounded end of a butter knife up the sides and across the top of the cake.
For the Cake
- 12 tablespoons (1 1/2 sticks) unsalted butter, room temperature, plus more for pans
- 2 1/2 cups all-purpose flour, plus more for pans
- 3/4 cup cocoa powder
- 1 teaspoon baking soda
- 1/4 teaspoon salt
- 1 cup granulated sugar
- 1 cup light-brown sugar
- 3 large eggs
- 2 teaspoons vanilla extract
- 1 1/2 cups buttermilk
For the Buttercream
- 1 cup (2 sticks) unsalted butter, room temperature
- 2 jars (7.5 ounces each) marshmallow cream
- 2/3 cup cocoa powder
- 2/3 cup semisweet chocolate chips, melted and cooled
- 1 tablespoon vanilla extract
Make the cake: Preheat oven to 350 degrees. Butter and lightly flour two 9-inch round cake pans. In a bowl, whisk flour, cocoa, baking soda, and salt.
In a mixing bowl, cream butter and sugars until fluffy. Add eggs, one at a time, beating until well incorporated. Beat in vanilla.
Add the flour mixture to the butter mixture in three additions, alternating with buttermilk and beginning and ending with the flour mixture. Scrape bowl as needed.
Pour batter into pans. Bake until toothpick inserted in center comes out clean, 25 to 30 minutes. Cool in pans 10 minutes before inverting cakes onto rack to cool completely.
Make the buttercream: In mixing bowl, beat butter and marshmallow cream until fluffy. Beat in cocoa, chocolate, vanilla, and 1 tablespoon water. If too thin, refrigerate about 5 minutes.
Place one layer on platter. Spread top with 1 cup buttercream. Place second layer on top. Frost entire cake with remaining buttercream.