Preheat oven to 175°C (350°F) and lightly grease and line two round cake pans
In a large bowl, whisk together flour, sugar, cocoa powder, baking powder, baking soda, and salt
In another bowl, blend together buttermilk, oil, eggs, and vanilla extract
Pour the wet mixture into the dry ingredients and stir gently until just combined
Pour in the hot coffee or hot water and stir until the batter is thin, glossy, and deeply chocolatey
Divide the batter between the prepared pans
Bake for 25-30 minutes until a toothpick comes out clean and the tops spring back softly
Cool the cake layers in their pans briefly, then transfer to a wire rack to cool completely
Pour warm heavy cream over the chocolate chips and let sit for a moment
Stir slowly until the chocolate melts into a silky glaze
Stir in butter for added shine and let the ganache cool slightly until it thickens
Spread ganache over the first cake layer
Place the second layer on top and pour remaining ganache over the edges and top of the cake
