Step 1

Preheat oven to 350°F. Butter two 8-by-2-inch round cake pans; dust with flour, tapping out excess. In a large bowl, whisk together flour, sugar, cocoa, baking powder, baking soda, and salt. Whisk in eggs, buttermilk, water, vanilla, and oil.

Step 2

Divide batter evenly between prepared pans. Bake until tops spring back when lightly pressed, about 30 minutes. Transfer pans to a wire rack; let cool 15 minutes. Invert cakes onto rack, remove parchment, then turn top-side up (to prevent sticky tops from sticking to rack); let cool completely.

Step 3

Spread 1 1/2 cups frosting over top of one cooled cake layer. Top with remaining layer. Spread a thin coat (about 1 cup) of frosting over top and sides of cake to create a “crumb coat.” Refrigerate about 20 minutes, then frost top and sides of cake with remaining frosting. (For a more refined look, trim domed top of cake flat before layering and frosting.)