1. Prepare the oven and pans.
Preheat the oven to 350°F (175°C). Grease three 8-inch round cake pans. Line the bottoms with parchment paper and lightly grease the parchment.

2. Combine the dry ingredients.
In a large bowl, whisk the flour, cocoa powder, granulated sugar, baking soda, baking powder, and salt. Break up any cocoa lumps.

3. Mix the wet ingredients.
In a separate bowl, whisk the eggs, buttermilk, vegetable oil, and vanilla until combined.

4. Make the batter.
Pour the wet mixture into the dry ingredients. Mix gently until mostly combined. Slowly add the hot coffee while whisking. The finished batter will be relatively thin. This is normal.

5. Divide the batter.
Divide evenly between the three pans. A kitchen scale gives the most even layers.

6. Bake.
Bake for 24–29 minutes. Begin checking at 24 minutes. A toothpick inserted into the center should come out without wet batter; a few moist crumbs are fine.

7. Cool completely.
Cool the cakes in their pans for 10–15 minutes. Turn them onto wire racks, remove the parchment, and cool completely before frosting.

8. Make the chocolate buttercream.
Beat the softened butter for 2–3 minutes until creamy. Gradually add the powdered sugar and cocoa on low speed. Add the heavy cream, vanilla, and salt. Beat until light and fluffy. If necessary, adjust with heavy cream one teaspoon at a time.

9. Level and fill the cake.
Trim large domes from the cooled cakes with a serrated knife if needed. Place the first layer on a cake board or serving plate. Spread with buttercream. Add the second layer, more buttercream, then the final cake layer.

10. Apply the crumb coat.
Cover the top and sides with a thin layer of chocolate buttercream. Refrigerate for 20–30 minutes, until firm and cold.

11. Prepare the ganache.
Place the finely chopped semisweet chocolate in a heat-safe bowl. Heat the cream until steaming and beginning to simmer around the edges. Pour it over the chocolate. Leave untouched for 2–3 minutes, then slowly stir until smooth.

12. Cool the ganache before pouring.
Let the ganache cool until thick but still pourable. Test one drip on the back of the chilled cake. If it runs immediately to the bottom, the ganache is still too warm.

13. Finish the cake.
Spread ganache across the top. Gently encourage a few irregular drips over the edge. Allow the ganache to settle.

14. Decorate.
Make curls from the dark chocolate with a vegetable peeler, or make thin chocolate shards. Arrange them loosely over the top.

15. Slice.
For cleaner slices, briefly chill the assembled cake. Use a sharp knife warmed with hot water and wiped completely dry before each cut.