Method

1. Preheat the oven to 220C/gas 7, and grease a large ovenproof serving dish.

2. For the mashed potato topping: bring a large pan of salted water to the boil over a high heat. Add the potatoes and boil for 15–20 minutes until tender. Drain well and mash with the butter until smooth, then set aside.

3. For the filling: melt half the butter with half the oil in a large saucepan over a medium heat. Add the onions, half the garlic and all the mushrooms and fry, stirring occasionally, for about 5 minutes, or until the onions are softened. Add salt and pepper to taste, then remove the pan from the heat and set aside.

4. Melt the remaining butter and oil in a large frying pan over a medium heat. Add the remaining garlic and salt and pepper and stir around. Add the lobster flesh and quickly toss it in the hot oil, then remove it from the pan and set aside.

5. Tip the scallops into the fat remaining in the pan, season them with salt and pepper and toss for 2–3 minutes, then remove and set aside.

6. Add the salmon to the pan and cook for 3–4 minutes. Remove it, reserving any fish juices, and separate the fish into large flakes. Gently combine all the filling ingredients in a large bowl.

7. For the cheese sauce: melt the butter in a pan over a low heat and stir in the flour to make a roux, then cook, stirring for a few minutes. Put any reserved fish juices into a measuring jug and make up to 850 ml with milk. Gradually whisk this liquid into the roux and bring it to the boil. Reduce the heat and cook the sauce until thickened, stirring constantly. Check the seasoning and then add the cheese, followed by the wine. The sauce should now have the consistency of thin custard.

8. Add the sacue to the fish mixture in the large bowl and mix everything together. Spoon it into the ovenproof dish. Spoon or pipe the mashed potato on top of the filling. Place the dish on a baking sheet and cook the pie for 30 minutes, until golden brown and bubbling.