Mornay sauce and a crunchy gratin topping combine to create a comforting fish dish. Serve with a green salad.
Place 4–6 small, shallow flameproof dishes on a baking tray.
For the gratin topping, mix the breadcrumbs, gruyere and parsley and set aside while you make the filling.
For the filling, pour the milk into a large, deep frying pan and add the onion, bay leaf and lemon peel. Place the fish skin-side down in the pan and bring to a gentle simmer over a medium heat. Baste the fish occasionally with the milk, and cook for 5–6 minutes. When cooked, the fish will be opaque and be starting to flake into pieces. Leave to stand for 5 minutes.
Drain the fish in a colander over a large jug, reserve the milk.
Melt the butter in a large non-stick saucepan and stir in the flour with a wooden spoon until thoroughly combined. Remove from the heat and slowly add the reserved warm milk, stirring constantly. Return to the heat, bring the sauce to a simmer and continue to stir until it is smooth and thick. Stir in the wine or vermout, Gruyère, mustard and cream. Cook over a low heat for a further 2–3 minutes, while stirring. Season with salt and freshly ground black pepper to taste.
Flake the fish into chunky pieces and discard the skin, onion, bay leaf and lemon peel. Add the fish to the pan with the sauce and heat very gently for a 2 minutes to warm it through.
While the fish is warming, preheat the grill to hot and place the baking tray with the shallow dishes under the heat to warm for a few seconds. Carefully remove them from the heat and divide the hot fish mixture between the warm dishes. Sprinkle with the gratin topping and return to the grill for 3–5 minutes or until nicely browned and filling bubbling undeneath.
This can be made in advance, chill the filling mixture covered in the fridge for a day, and then fill the ovenproof dishes and sprinkle with the topping just before grilling.
