Yield 24 cupcakes

1 cup stout (such as Guinness)
1 cup (2 sticks) unsalted butter
3/4 cup unsweetened cocoa powder (preferably Dutch-process)
2 cups all purpose flour
2 cups sugar
1 1/2 teaspoons baking soda
1 teaspoon baking powder
3/4 teaspoon salt
2 large eggs
2/3 cup sour cream

Preheat oven to 350°F. Line 24 cupcake cups with liners. Bring 1 cup stout and 1 cup butter to simmer in heavy large saucepan over medium heat. Add cocoa powder and whisk until mixture is smooth. Cool slightly.
Whisk flour, sugar, baking soda, baking powder and 3/4 teaspoon salt in large bowl to blend. Using electric mixer, beat eggs and sour cream in another large bowl to blend. Add stout-chocolate mixture to egg mixture and beat just to combine. Add flour mixture and beat briefly on slow speed. Using rubber spatula, fold batter until completely combined. Divide batter among cupcake liners, filling them 2/3 to 3/4 of the way. Bake cake for about 17 minutes or until tester inserted into center comes out clean, rotating them once front to back if your oven bakes unevenly. Cool cupcakes on a rack completely.

Bailey’s Frosting

3 to 4 cups confections sugar
1 stick (1/2 cup or 4 ounces) unsalted butter, at room temperature
3 to 4 tablespoons Baileys (or milk, or heavy cream, or a combination thereof)
Whip the butter in the bowl of an electric mixer, or with a hand mixer, for several minutes until fluffy and light.. Slowly add the powdered sugar, a few tablespoons at a time.
When the frosting looks thick enough to spread, drizzle in the Baileys (or milk) and whip it until combined. If this has made the frosting too thin (it shouldn’t, but just in case) beat in another spoonful or two of powdered sugar.
Ice and decorate.