Butter two 8 inch round cake pans. Line with parchment paper and then butter the paper. Lightly flour both pans and set aside.

In a stand mixer, briefly combine the flour, sugar, cocoa, baking soda, baking powder, and salt.

In a separate bowl, whisk together the buttermilk, eggs, oil, and vanilla.

Add the buttermilk mixture to the dry ingredients and blend until just combined.

Slowly beat in the hot coffee. Do not overmix.

Divide the batter into the two prepared pans and bake at 350 degrees for approximately 35 minutes, or until a tester inserted in the middle of the cake comes out clean.

Allow the cakes to cool for about 30 minutes in the pans and then invert onto cooling racks to finish cooling completely.

Melt the chocolate gently in the microwave, in 30 second intervals. Set aside to cool for a few minutes.

Using an electric mixer with paddle attachment, beat the butter on medium until light and fluffy.

Add the egg yolk and vanilla and beat for an additional minute.

Scrape down the sides of the bowl.

On low speed, slowly add in the powdered sugar until just combined.

Dissolve the coffee granules in the hot water and slowly add the slurry and the cooled chocolate into the frosting mixture, beating just to combine.

On the plate or stand of your choice, place one of the cake layers flat side up. Apply a layer of frosting to the top and add the second cake layer.

Coat the cake generously in your frosting and, if desired, dust with chocolate shavings.

Refrigerate for at least one hour before serving.