2 lbs. fresh or frozen, thawed white fish, such as cod or sole, fillets - buy the thickest ones available
1/2 tsp. salt
1/8 tsp. white or black pepper
6 tbsp. butter
1 med. onion, chopped
3 c. fresh bread crumbs, not dried
1 c. grated Cheddar cheese
1/4 c. fresh parsley
1 tsp. dry mustard

Preheat oven to 350 degrees. Lightly grease a 9 x 12 inch oven proof glass baking dish. Season fillets with salt and pepper. Arrange fillets on baking dish. Melt butter in large skillet over medium-low heat. Add remaining ingredients and mix well. Spread topping over fillets. Bake until fish is opaque and flakes easily and topping is golden brown, 20-25 minutes. Serve immediately. Makes 6 servings.