Cod au Gratin

• 1 lb cod fillets, cubed
• 1/4 cup butter
• 1/4 cup flour
• 1 1/4 cups milk
• 1 tsp salt
• Pepper to taste
• 1 small onion, finely chopped
• 1/2 cup breadcrumbs
• 1/2 cup cheddar cheese, grated

Preheat oven to 375º F. Place cod in a greased baking dish. Make the béchamel sauce in a heavy saucepan by first melting butter, then stirring in the flour until smooth. Remove from heat and gradually stir in half the milk. Return to heat and beat until smooth and shiny. Gradually add remaining milk, salt, pepper and onion. Cook, stirring, until sauce is smooth and thickened. Pour sauce over fish and sprinkle breadcrumbs and cheese over the top. Bake uncovered for 15-30 minutes until sauce bubbles and cheese begins to brown, and fish is completely cooked.