Preheat the oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.

In a mixing bowl, whisk together flour, sugar, cocoa powder, baking powder, baking soda, and salt.

Add buttermilk, vegetable oil, eggs, and vanilla extract to the dry ingredients. Mix until combined.

Stir in boiling water until the batter is smooth. Pour the batter evenly into the prepared pans.

Bake for 30-35 minutes or until a toothpick inserted in the center comes out clean. Let cool in pans for 10 minutes, then remove from pans and cool completely on a wire rack.

In a mixing bowl, beat the softened butter until creamy.

Gradually add cocoa powder and powdered sugar, alternating with milk, until the desired consistency is reached.

Stir in vanilla extract. Frost the cooled cake layers and stack them.