Combine Dry Ingredients: In a large mixing bowl, whisk together all-purpose flour, granulated sugar, cocoa powder, baking powder, baking soda, and salt.

Add Wet Ingredients: Add milk, eggs, vegetable oil, and vanilla extract to the dry mixture and whisk until just combined.

Incorporate Hot Coffee: Gradually whisk in hot black coffee until the batter is smooth and glossy.

Prepare to Bake: Preheat oven to 350°F (175°C) and grease two 9-inch round cake pans. Divide the batter evenly between the pans.

Bake the Cakes: Bake for 20-25 minutes, until a toothpick inserted in the center comes out clean.

Cool Cakes in Pans: Let cool in pans for 10 minutes before transferring to a wire rack.

Make the Fudgy Buttercream Frosting: Sift powdered sugar and cocoa powder, then mix with softened butter and milk until creamy.

Frost the Cakes: Once cool, layer frosting on the cake and cover the entire cake with remaining frosting.