This Newfoundland and Labrador home-style casserole pairs flaky Atlantic cod with a smooth onion-and-cheddar sauce and a crisp breadcrumb top. The recipe is one practical variation: household and historical versions differ in how they cook the fish and finish the gratin.
Cod au gratin is associated with Newfoundland and Labrador home cooking and appears in regional recipes for generations. Some versions cook and flake the fish before layering it with sauce; others bake raw cod under a creamy topping. This edition uses fresh or fully thawed Atlantic cod, a simple béchamel with onion and cheddar, and buttered breadcrumbs. The fish’s centre temperature, rather than browning alone, determines when it is ready.
Step 1Heat the oven to 190°C / 375°F. Pat the cod dry and cut it into 4–5 cm pieces. Lightly butter a shallow 2-litre baking dish if needed.
Step 2Melt the 30 g butter in a saucepan over medium heat. Add the onion and cook for 4–5 minutes until soft but not browned. Stir in the flour and dry mustard; cook for 1 minute.
Step 3Gradually whisk in the warm milk until smooth. Simmer, whisking, for 3–5 minutes until the sauce coats a spoon. Take the pan off the heat and stir in 80 g cheddar, salt and pepper.
Step 4Arrange the cod in the baking dish and pour the sauce over it. Mix the breadcrumbs with the melted 15 g butter and remaining 40 g cheddar, then scatter the mixture evenly over the top.
Step 5Bake uncovered for 25–30 minutes, until bubbling and browned and the thickest cod piece reaches 70°C / 158°F at its centre. Rest for 10 minutes before serving.
Serve the casserole hot with peas, green beans or a crisp salad. A shallow dish helps the fish cook evenly. If the cod is frozen, thaw it completely in the refrigerator before starting; do not put frozen blocks under the sauce. Keep raw fish separate from ready-to-eat foods and wash hands, utensils and surfaces after handling it.
Cool leftovers promptly in a shallow covered container and refrigerate within 2 hours. Use within 2–3 days or freeze. Reheat leftovers until the centre reaches 74°C / 165°F. The gratin can be assembled shortly ahead and refrigerated, but allow extra oven time for a cold dish and verify the fish temperature.
These rounded values are an ingredient-based estimate for one of 4 portions. Fish, cheese, milk and breadcrumb labels differ, so actual values—especially sodium—will vary.
Contains fish, milk, wheat and mustard. Check package labels for additional allergens and cross-contact warnings. Keep raw fish separate from ready-to-eat food, thaw it in the refrigerator and cook the thickest piece to 70°C / 158°F. Refrigerate leftovers within 2 hours, use within 2–3 days or freeze, and reheat to 74°C / 165°F.
Yes. Thaw it completely in the refrigerator, drain any liquid and pat the fish dry before assembling the dish.
