adapted from Ina Garten

Cake:

Butter, for greasing the pans

1 3/4 cup flour, plus more for pans

2 cups sugar

3/4 cup cocoa powder

2 teaspoons baking soda

1 teaspoon baking powder

1 teaspoon salt

1 cup buttermilk

1/2 cup vegetable oil

2 eggs

2 teaspoons vanilla

1 cup freshly brewed hot coffee

Frosting:

6 oz. semi sweet chocolate

1/2 pound unsalted butter, at room temperature

1 egg yolk

1 teaspoon vanilla

1 1/4 cup powdered sugar

1 tablespoon instant coffee powder

For the cake: 

Preheat oven to 350.  Butter 2 (8-inch) round cake pans.  Line the pans with parchment paper.  Butter and flour the parchment paper, shaking out the excess flour.  Sift the flour, sugar, cocoa powder, baking powder, baking soda and salt into the bowl of an electric mixer.  Mix on low speed until well combined.  

In a separate bowl, combine the buttermilk, oil, eggs, and vanilla.  With the mixer on low speed, slowly add the wet ingredients into the dry ingredients.  With the mixer on low, slowly add the coffee and mix just to combine - scraping the bowl with a spatula.  (Don't worry - the batter will be very liquidy).  Pour the batter into the prepared pans and bake for 35 to 40 minutes.  Turn out onto a cooling rack to cool completely.

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

For the frosting: 

Chop the chocolate and place it in a heat proof bowl that is set over a pot of simmering water.  Stir until just melted.  Set aside and let cool to room temperature.

In the bowl of an electric mixer, beat the butter on high speed until light and fluffy - about 3 minutes.  Add the egg yolk and vanilla and continue mixing - another 3 minutes.  Turn the mixer speed to low, slowly add the powdered sugar to the mixture - scraping down the bowl until smooth and creamy.  

Dissolve the coffee powder into 2 teaspoons of hot water.  On low speed, add the chocolate and coffee to the butter mixture and mix until blended.  Spread immediately on the cooled cake.