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

In a second bowl, whisk the eggs, buttermilk, oil, and vanilla. Pour the wet ingredients into the dry ingredients and stir just until no dry streaks remain.

Slowly pour in the hot espresso while whisking gently. The batter will be thin, which is expected and helps create a moist cake.

Divide the batter between the prepared pans. Bake for 26 to 30 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, then turn them onto wire racks. Remove the parchment and cool completely before frosting.

Place the chopped chocolate in a heatproof bowl. Warm the cream until steaming but not boiling, pour it over the chocolate, and let it stand for 3 minutes.

Stir the chocolate and cream from the center outward until glossy. Add the butter and vanilla, then stir until smooth. Cool the ganache until thick enough to spread, about 45 to 75 minutes.

Place one cake layer on a serving plate. Spread about one-third of the ganache over the top, add the second layer, and cover the top and sides with the remaining ganache.

Finish with chocolate curls and a light dusting of cocoa powder. Chill for 30 minutes for neat slices, then serve slightly cool or at room temperature.