Put beer, onion, celery, parsley, salt and pepper in a skillet. Heat to boiling and add fish. Cover and simmer about 8-10 minutes, or just until fish flakes with a fork. Drain fish and put onto deep platter. Place in a 300 degree oven to keep warm. Boil cooking liquid about 5 minutes to reduce and strain. In the top of a double boiler, beat egg yolks with cream. Gradually stir in 1/2 C hot strained cooking liquid. Cook over boiling water, stirring constantly, until thickened. Cut butter into small pi eces and stir into sauce, one piece at a time. Pour sauce over fish. Makes 3-4 servings