01 - Preheat oven to 350°F. Grease three 8-inch round cake pans and line bottoms with parchment paper.
02 - Sift flour, cocoa powder, sugar, baking powder, baking soda, and salt into a large mixing bowl.
03 - Whisk buttermilk, hot coffee, vegetable oil, eggs, and vanilla extract in a separate bowl until fully incorporated.
04 - Pour wet ingredients into dry mixture. Stir until just combined, being careful not to overmix the batter.
05 - Divide batter evenly among prepared pans. Smooth tops using an offset spatula.
06 - Bake for 30–35 minutes until a toothpick inserted into center emerges clean.
07 - Let cakes rest in pans for 10 minutes, then invert onto wire racks to cool completely.
08 - Beat butter until creamy. Gradually incorporate powdered sugar and cocoa on low speed. Add milk, vanilla, and salt. Whip until fluffy, adjusting consistency with additional milk if necessary.
09 - Heat heavy cream in small saucepan until simmering. Pour over chopped chocolate and butter in heatproof bowl. Let stand 2 minutes, then whisk until glossy and smooth. Cool until thickened but pourable.
10 - Place first cake layer on serving plate. Spread frosting evenly. Add second layer and frost again. Position third layer and coat top and sides with remaining frosting.
11 - Pour ganache over cake center, allowing it to cascade down sides for dramatic finish.
12 - Refrigerate 20–30 minutes until ganache sets. Slice and serve at room temperature.