Heat the oven to 350°F (175°C). Grease two 9-inch round cake pans, line the bottoms with parchment, and lightly dust the sides with cocoa powder.

Whisk the flour, sugar, cocoa powder, baking soda, baking powder, and salt in a large mixing bowl until evenly combined.

Add the eggs, buttermilk, oil, and vanilla. Whisk for about 1 minute, just until the mixture is smooth and no dry streaks remain.

Slowly pour in the hot coffee while whisking. The batter will be thin, which is exactly what produces a moist, tender cake.

Divide the batter evenly between the prepared pans. Bake for 28 to 32 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.

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

For the buttercream, beat the softened butter until creamy. Add the confectioners' sugar and cocoa powder gradually, then mix in the cream, vanilla, and salt until fluffy and smooth.

Place one cake layer on a serving plate. Spread a generous cup of frosting over the top, add the second layer, and frost the top and sides. Finish with chocolate shavings if desired.