Prick bratwurst on both sides, put in skillet with enough boiling water to cover. Cover and simmer 5 minutes. Drain water, add 2 tablespoons butter and brown bratwurst. Add beer and some water to cover bratwurst, bring to boil, reduce heat and simmer 25 minutes. Remove cover and burn off about 1/2 of liquid. In different pan: melt 2 tablespoon butter and saute' onions to brown. Blend in flour until the color of cocoa. Add to simmering ale and blend until smooth and thick. Serve.