Thaw fish. Preheat broiler. Place in a single layer on a greased, unheated rack of broiler pan or in a greased baking pan. Brush with half of the melted butter; sprinkle with 1 teaspoon salt and dash pepper.
Broil fish 4 inches from heat 5 to 8 minutes; turn. Brush with remaining melted butter. Broil 5 to 8 minutes longer or till fish flakes easily with a fork.
In a saucepan cook onion and garlic in 1 tablespoon butter till tender. Stir flour into sour cream; stir in broth. Add to saucepan. Cook and stir till bubbly. Drain mushrooms. Stir mushrooms and sherry into sauce; heat through.
Serve sauce over fish.
Yield: 6 Servings