Ingredients

Step by step

1. Heat the oven to 200°C, fan 180°C, gas 6. Cook the potatoes in boiling salted water for 12-15 minutes. Drain and leave to steam dry in the pan while you make the fish pie filling.
2. Put the frozen fish into a wide pan in a single layer. Pour over the milk and add the bay leaf. Add 250ml water, so it almost covers the fish, and bring to a simmer. Cook for 2 minutes, until the fish is starting to flake, then carefully remove to a plate with a slotted spoon. Pour the milk off into a large jug, then measure 700ml back into the pan.
3. Put the cornflour into a mug and add a few spoons of the milk from the pan. Mix really well to remove any lumps and make a thick paste, then add back to the pan, stirring well. Cook for 5-8 minutes over a medium heat until the sauce thickens, continually stirring. Add the parsley, peas, broad beans and spinach. Warm through for a few minutes, then remove from the heat.
4. Mash the potatoes, adding the milk to get a lovely smooth, velvety mash. Season well.
5. Flake the cooked fish and add to the white sauce along with the prawns. Season well, adding lemon juice to taste. Spoon into an ovenproof baking dish and top with the mash. Use a fork to swirl the top of the pie. Dot over the butter in small pieces. Put the dish on a baking tray and bake for 25 minutes until bubbling. Grill for the last few minutes if you want a crisp, golden top.