1/4 cup cocoa powder (to dust the baking pans)
2 sticks butter
1 cup Guinness
2/3 cup Dutch process dark cocoa powder
1 teaspoon salt
2 cups unbleached flour
2 cups sugar
1 1/4 teaspoon baking soda, sifted
2 large eggs
1/2 cup sour cream
Heat oven to 350° F.
Lightly dust two greased 8 inch springform pans with cocoa powder. In a heavy saucepan or microwave oven, heat butter, beer, and cocoa powder until butter melts. Let cool. Sift dry ingredients together.
Add the beer-cocoa mixture, and beat thoroughly for 1 minute on medium speed. Add the eggs and sour cream and beat 2 minutes on medium speed. Pour batter into prepared pans and bake for 25 to 30 minutes or until a toothpick inserted into the middle comes out clean.
Place pans on a wire rack, cool for 10 minutes, remove the sides, and cool completely. Use a long serrated knife to even the tops of the cakes.
Using a flexible spatula, spread each layer with a thin coating of chocolate frosting, stack, and cover the sides with frosting.