Heat the oven to 350°F. Grease two 9-inch round cake pans, line the bottoms with parchment, and lightly dust the sides with cocoa powder.

Whisk flour, cocoa powder, sugar, baking soda, baking powder, and salt in a large bowl. Break up every cocoa lump so the finished crumb is smooth.

In another bowl, whisk eggs, buttermilk, oil, and vanilla until blended. Pour the wet mixture into the dry mixture and stir just until no dry streaks remain.

Slowly pour in the hot coffee while whisking gently. The batter will be thin, and that loose texture is what helps produce a moist cake.

Divide the batter between the prepared pans. Bake for 27 to 31 minutes, or until the centers spring back lightly and a toothpick comes out with a few moist crumbs.

Cool the cakes in their pans for 10 minutes, then turn them onto wire racks. Remove the parchment and cool completely before frosting.

Beat softened butter until creamy, then add cocoa powder, powdered sugar, cream, vanilla, and salt in stages. Beat for 2 to 3 minutes until smooth, fluffy, and spreadable.

Place one cake layer on a stand and spread it with frosting. Add the second layer, cover the top and sides, then garnish with chocolate curls or a light cocoa dusting.