Cod au Gratin

1 pound cod fillets, cut in serving pieces 1/4 cup butter 1/4 cup all-purpose flour1 1/4 cups milk1 teaspoon saltPepper to taste1 small onion, finely chopped 1/2 cup bread crumbs or cracker crumbs 1/2 cup cheddar cheese, gratedHeat oven to 375 degrees.Place cod pieces in greased baking dish.In heavy saucepan, melt butter and stir in flour until smooth. Remove from heat and gradually add half the milk, return to heat and beat until smooth and shiny. Slowly add remaining milk, salt, pepper and onion. Cook, stirring, until smooth and thickened.Pour sauce over fish and sprinkle with bread crumbs and cheese. Bake 20-25 minutes or until sauce bubbles and fish flakes.Serves four.Nutrition values per serving: 387 calories, 20 g fat (12 g saturated), 21 g carbohydrates, 1 g fiber, 29 g protein, 98 mg cholesterol, 905 mg sodium.