01 - Preheat oven to 350°F. Grease three 8-inch round cake pans and line 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 well combined.
04 - Pour wet ingredients into dry mixture. Mix until just combined; avoid overmixing to maintain tender texture.
05 - Divide batter evenly among prepared pans. Smooth tops with spatula.
06 - Bake for 30 to 35 minutes, until toothpick inserted in center comes out clean.
07 - Cool in pans for 10 minutes, then transfer to wire racks to cool completely.
08 - Beat butter until creamy. Gradually add powdered sugar and cocoa powder on low speed. Incorporate milk, vanilla, and salt. Beat until fluffy, adjusting consistency with additional milk if necessary.
09 - Heat cream in saucepan until just simmering. Pour over chopped chocolate and butter. Let stand 2 minutes, then whisk until smooth. Cool until thickened but pourable.
10 - Place first cake layer on serving plate. Spread with frosting. Add second layer and frost again. Position third layer and frost top and sides completely.
11 - Pour ganache over top center, allowing it to cascade down sides for dramatic presentation.
12 - Refrigerate for 20 to 30 minutes to set ganache before slicing.