For the Cake:
1½ cups stout or dark beer, such as Guinness
1½ cups unsalted butter
1 cup Dutch-process cocoa powder
3 cups all-purpose flour
3 cups granulated sugar
2¼ teaspoons baking powder
1 teaspoon salt
2/3 cup sour cream
For the Frosting:
16 ounces cream cheese, at room temperature
½ cup butter, at room temperature
7 tablespoons Baileys Irish Cream
6 cups powdered sugar
1. Preheat the oven to 350°F. Grease and flour two 9-inch cake pans, and line them with parchment paper circles.
2. Place the stout and butter in a large, heavy saucepan, and heat until the butter melts. Remove the pan from the heat, and add the cocoa powder. Whisk until the mixture is smooth. Set aside to cool to room temperature.
3. Whisk together the flour, sugar, baking powder, and salt in a large bowl; set aside.
4. In a large mixing bowl, beat together the eggs and sour cream. Add the stout-cocoa mixture, mixing to combine. Add the flour mixture and mix together at slow speed. Scrape the sides and bottom of the bowl, and mix again for 1 minute.
5. Divide the batter equally among the prepared pans. Bake the layers for 35 minutes, until a cake tester inserted into the center comes out clean. Remove the cakes from the oven and cool on a rack for 10 minutes before turning the cakes out of their pans and returning to the rack to finish cooling completely before frosting.
6. Make the Frosting: In a mixing bowl, blend together the cream cheese, butter, and Baileys Irish Cream on medium speed until completely smooth and combined. Gradually add the powdered sugar on medium-low speed until it has all been added. Increase the speed to medium-high and beat until the frosting is smooth and thoroughly mixed. Use immediately. You can refrigerate the frosting, but it will need to be brought to room temperature before using. This yields enough frosting to fill the cake and frost the outside, and do some basic decorations.
*Note: If the finished frosting is a little soft for your liking, you can add more powdered sugar, a tablespoon at a time, until you reach the desired consistency.