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 extract in a separate bowl until well combined.
04 - Pour wet ingredients into dry mixture. Mix until just combined; avoid overmixing to prevent tough texture.
05 - Divide batter evenly among prepared pans. Smooth tops with an offset spatula.
06 - Bake for 30-35 minutes, or until a wooden toothpick inserted into the center comes out clean.
07 - Let cakes cool in pans for 10 minutes, then invert onto wire racks to cool completely before frosting.
08 - Beat softened butter until creamy. Gradually add powdered sugar and cocoa powder on low speed. Pour in milk, vanilla, and salt. Beat until fluffy and spreadable, adding extra milk if necessary.
09 - Heat heavy cream in a small saucepan until just simmering. Pour over chopped chocolate and butter in a heat-proof bowl. Let stand for 2 minutes, then whisk until smooth and glossy. Cool until thickened but still pourable.
10 - Place first cake layer on a serving plate. Spread generous layer of frosting over top. Position second layer and repeat frosting. Add third layer and apply frosting to top and sides of entire cake.
11 - Pour cooled ganache over the top of the cake, allowing it to cascade down the sides for a dramatic dripping effect.
12 - Refrigerate assembled cake for 20-30 minutes to set ganache before slicing and serving.