Step 1

Preheat the oven to 350 degrees F. Butter two 8-inch x 2-inch round cake pans. Line with parchment paper, then flour the pans.

Step 2

Sift the flour, sugar, cocoa, baking soda, baking powder, and salt into a large mixing bowl. Whisk until combined. In another bowl, combine the buttermilk, oil, eggs, and vanilla. Add the wet ingredients to the dry. Add the coffee and stir just to combine. Batter will be really thin. Pour the batter — if you feel like being really precise, pour about 690g of batter into each pan — into the prepared pans and bake for 35 to 40 minutes, until a cake tester comes out clean. Cool in the pans for 30 minutes, then turn them out onto a cooling rack and cool completely.

Step 3

To make the frosting: Chop the chocolate and place it in a heat-proof bowl set over a pan of simmering water. Stir until just melted and set aside until cooled to room temperature. Alternatively: Melt in the microwave at 30 second to 1-minute intervals until spreadable.

Step 4

In the bowl of an electric mixer fitted with a paddle attachment, beat the butter on medium-high speed until light yellow and fluffy, about 3 minutes. Add the vanilla and continue beating for 3 minutes. Turn the mixer to low, gradually add the confectioners’ sugar, then beat at medium speed, scraping down the bowl as necessary, until smooth and creamy. On low speed, add the chocolate to the butter mixture and mix until blended. Don’t whip. Spread immediately on the cooled cake.

Step 5

Place 1 layer, flat side up, on a flat plate or cake pedestal. With a knife or offset spatula, spread the top with frosting. Place the second layer on top, rounded side up, and spread the frosting evenly on the top and sides of the cake.