Preheat oven to 350°F (175°C). Grease and flour two 9-inch round cake pans or one 9×13-inch pan.

1. In a medium bowl, whisk together flour, cocoa powder, baking powder, baking soda, and salt.
2. In a large mixing bowl, cream butter, granulated sugar, and brown sugar until light and fluffy.
3. Add eggs one at a time, beating well after each addition. Mix in vanilla extract and Irish cream.
4. Mix in the sour cream until well combined.
5. Alternately add the dry ingredients and brewed coffee to the wet mixture, beginning and ending with dry ingredients. Mix until just combined.
6. Divide the batter between prepared pans and smooth the tops.
7. Bake for 30–35 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.
8. Cool cakes in pans for 10 minutes, then transfer to a wire rack to cool completely.
9. For the ganache: Heat heavy cream until just simmering, then pour over chocolate.
10. Let sit for 1–2 minutes, then stir until smooth. Add Irish cream and butter, stirring until glossy.
11. Let ganache cool slightly until thickened but still pourable. Spread or pour over cooled cake.