Meanwhile, in 2-quart saucepan over medium heat, melt 1/4 cup butter. Stir in brown sugar. Heat to boiling, stirring constantly; reduce heat to low. Boil and stir 2 minutes. Stir in 2 tablespoons beer. Heat to boiling; remove from heat. Cool to lukewarm, about 20 minutes. Stir in powdered sugar. Add additional beer, 1 teaspoon at a time until soft and spreadable. Spoon over top of cake, allowing some to run down side of cake. Sprinkle with beer nuts.