Chocolate ganache frosting:

1. Finely chop semi-sweet chocolate. Place in a medium size bowl.
2. Cook heavy cream in a small pot over low-medium, stirring constantly, until simmering and steaming.
3. Pour hot cream over chocolate. Allow to sit for 2-3 minutes.
4. Using a spatula, stir smooth. Cover with plastic wrap and allow to set until room temperature.

Chocolate coffee cake:

1. Combine the semi-sweet chocolate and milk in a small bowl.
2. Microwave for 20-30 seconds until milk is hot. Whisk until smooth.
3. Add the espresso powder and whisk until combined. Stir in the remaining wet ingredients (sour cream, vanilla extract and vegetable oil).
4. In a separate bowl, stir together the dry ingredients (flour, baking cocoa, baking powder and salt).
5. In the bowl of a stand mixer, combine the eggs and sugar. Whip on high until light and fluffy (2-3 minutes).
6. Pour half of the dry ingredients into the egg mixture and whip on low until just combined.
7. Add the wet ingredients, mixing until just combined.
8. Add the remaining dry ingredients, mixing on low until the batter is free of lumps.
9. Pour the batter into a parchment paper-lined square 8" pan.
10. Bake at 350F for 30-35 minutes or until a toothpick inserted in the center comes out with only baked crumbs (no batter). Allow the cake to cool in the pan.

Cake assembly:

1. Whip the cooled ganache on medium-high until stiff peaks form and the frosting is a light brown (about 2-3 minutes).
2. Remove the cooled cake from its pan.
3. Spoon the frosting on top of the cake and spread evenly.