Preheat oven to 325°F. Butter three 8-inch cake pans. Line the bottom of each pan with parchment and butter again.

In a medium bowl, sift together flour, cocoa, baking powder, baking soda, and salt. Re-sift and set aside.

In a heatproof bowl, pour hot coffee over chocolate. Let stand 3 minutes, then whisk until smooth. Add buttermilk and whisk to combine. Set aside.

In the bowl of a stand mixer fitted with the whisk attachment, combine oil, brown sugar, and sugar. Beat on medium-low until combined, about 1 minute. With the mixer still on medium-low, add the eggs, one at a time, waiting until each is completely incorporated before adding the next. Add the vanilla and mix in.

Turn the mixer to low and add half the flour mixture, followed by half the buttermilk. Add remaining flour mixture, followed by the remaining buttermilk. Mix until smooth.

Divide the batter among the prepared pans (each pan should have about 490g of batter) and bake until the cake springs back when pressed lightly in the center and a skewer inserted into the center comes out clean, about 30 to 35 minutes.

Let cool 20 minutes before running a sharp knife around the edge and removing the layers from the pans to cool completely.