01 - Preheat oven to 350°F. Grease and line three 8-inch round cake pans with parchment paper.
02 - Sift together flour, cocoa powder, sugar, baking powder, baking soda, and salt in a large bowl.
03 - Whisk buttermilk, hot coffee, oil, eggs, and vanilla in a separate bowl until fully incorporated.
04 - Pour wet ingredients into dry mixture. Stir until just combined; avoid overmixing to maintain tender crumb.
05 - Divide batter evenly among prepared pans. Smooth tops with spatula. Bake for 30-35 minutes until toothpick inserted in center comes out clean.
06 - Let cakes rest in pans for 10 minutes, then invert onto wire racks to cool completely before frosting.
07 - Beat softened butter until creamy. Gradually incorporate powdered sugar and cocoa powder on low speed. Add milk, vanilla, and salt. Whip until fluffy and spreadable, adjusting consistency with additional milk if necessary.
08 - Heat heavy cream in small saucepan until just simmering. Pour over chopped chocolate and butter in a heat-proof bowl. Let stand for 2 minutes, then whisk until completely smooth. Allow to cool until thickened but still pourable.
09 - Place first cake layer on serving plate. Spread frosting evenly over surface. Position second layer on top and frost. Add third layer and apply frosting to top and sides of entire cake.
10 - Pour prepared ganache over top of cake, allowing it to cascade down sides for dramatic presentation.
11 - Refrigerate assembled cake for 20-30 minutes to set ganache before slicing and serving.