Step 1

Heat the oven to 180C/fan 160C/gas Gently cook the leeks in half the butter until really soft. Stir in the flour and cook for a couple of minutes. Gradually stir in the wine until you have a sauce and simmer for 5 minutes. Add the cream and bring gently to a simmer for a couple of minutes. Stir in the parsley, fish and prawns, then take off the heat. Tip into a baking dish.

Step 2

To make the mash, boil the potatoes in salted water until tender. Drain, then tip back into the pan over a low heat to dry out slightly. Add the rest of the butter, a splash of milk and some seasoning. Mash really well. Spoon over the fish, then spread out using a fork so you end up with a rough surface. Dot or brush with more butter for a golden top.

Step 3

Bake the pie in the oven for 30-35 minutes until the top is crisp and golden, and the filling is bubbling and piping hot.

Step 4

To freeze the pie, cover with clingfilm and freeze after assembling (but before cooking) for up to 2 months. Defrost completely in the fridge overnight. Cook following the instructions above.