1 cup plus 4 tablespoons (2 1/2 sticks) unsalted butter, plus more for pans
2 cups all-purpose flour
1 3/4 cups granulated sugar
3/4 cup cacao powder
2 teaspoons baking soda
1 1/2 teaspoons baking powder
1/2 teaspoon kosher salt
1/4 cup packed brown sugar
2 large eggs, at room temperature
1 cup whole-fat buttermilk, at room temperature
1/2 teaspoon vanilla extract
3 ounces bittersweet chocolate
Chocolate Buttercream (recipe follows)
1/2 cup (1 stick) unsalted butter, at room temperature
1/3 cup cacao powder
1/8 teaspoon kosher salt
2 cups confectioners’ sugar
1/4 cup whipping cream
Reserved melted chocolate (from cake recipe)
Preheat the oven to 350°F. Prepare three 6-inch cake pans by buttering the insides and lining the bottom with a piece of parchment paper.
Create a double-boiler by filling a medium pot one-third of the way full with water. Place a medium stovetop-safe bowl atop the pot. Bring to a simmer over medium-low heat. As the double-boiler warms, on a cutting board, rough chop the chocolate into small pieces (or break using your hands). Drop the chocolate into the bowl atop the double-boiler. Using a rubber spatula, occasionally move the chocolate as it melts. Once no clumps are visible and the chocolate is thoroughly melted and glossy in appearance, remove off the heat. Reserve half of the melted for the frosting. Set atop a wire cooling rack and allow to cool for 10 minutes.
In a small pot over low heat or a microwave-safe bowl, melt your butter. Set aside.
Place a sifter into a large bowl and sift together the flour, granulated sugar, cacao, baking soda, baking powder, and salt.
In a stand mixer using the whisk attachment, combine the warm butter and brown sugar. Whisk on medium-low until the brown sugar has dissolved. Mixing on medium speed, add in the eggs one at a time. Mix until the eggs are emulsified into the butter mixture. Add in the portion of the melted chocolate and mix on high speed for 1 minute, then add the vanilla extract. In 3 batches, alternate pouring in the dry ingredients and buttermilk, beating on low and scraping down the sides. Gather 1/4 cup warm water from the pot of the double boiler. Then, pour in the reserved warm water. Mix until fully incorporated. The texture should appear smooth and shiny.
Pour the batter equally amongst the pans and place in the oven to bake for 30 to 35 minutes, until a toothpick comes out clean (minimal chocolate crumbles are fine). Once complete, remove from the oven and allow to cool atop a wire rack until fully cooled. Once room temperature to touch, place the cooling rack atop the exposed part of the cake pan. Then, carefully flip the cake onto the cooling rack. The cake should slide out easily. Frost your cake and enjoy!
In a stand mixer using the paddle attachment, drop in the butter, cacao powder, and salt. Beat together on medium speed until cohesive. Next, add in the confectioners’ sugar, 1 cup at a time, mixing on low. Make sure to scrape down the sides. The mixture will be chalky and bulky in appearance. Pour in the reserved melted chocolate and beat on medium for 1 minute. Next, mixing on low, pour in the whipping cream. After it begins to incorporate, increase the speed and beat on high for 3 minutes. Makes about 2 cups.