Drain oysters; reserve liquor. Melt butter; saute onion and celery until soft and golden. Blend in 2 tablespoons flour. Gradually stir in oyster liquor and milk. Add salt, mace, black pepper, nutmeg and cayenne pepper. Blend in 3 tablespoons flour and cook, stirring constantly until mixture comes to boil and thickens. Add oysters to sauce; heat until oysters plump and edges curl. Do not boil. Spoon about 1/2 cup oyster mixture into each patty shell. Serve immediately. Makes 8 servings, 2 patty shells each.