For the Cake
Preheat oven to 350°F.
Bring 2 cups stout and 2 cups butter to simmer in a saucepan over medium heat.
Add cocoa powder and whisk until mixture is smooth. Set aside to cool.
In a medium bowl, whisk flour, sugar, baking soda, and salt in large bowl.
Using electric mixer, beat eggs and sour cream in a large bowl.
Add stout-chocolate mixture to egg mixture and beat just to combine.
Add flour mixture in thirds and beat briefly on slow speed
Divide batter among two round 9 inch cake pans, buttered, floured, and lined with parchment paper.
Bake until tester inserted into center of cakes comes out clean, about 40 minutes.
For The Frosting
Cream butter and cream cheese in a large bowl with an electric mixer until smooth.
Add powdered sugar in increments until smooth. Add Irish cream flavor and whisk until well blended.