The best fish pie

Step 1

Put the potatoes into a saucepan and cover with boiling water. Simmer for 15-20 minutes until tender when poked with a knife, then drain and set aside.

Step 2

Place a large saucepan over a medium heat. Add the 75g butter and, when melted, tip in the leeks. Sauté until soft, 4-5 minutes, then stir in the garlic and cook for 2 minutes more.

Step 3

Sprinkle the flour into the leeks, stir until coated, then gradually add the white wine. Cook for 1-2 minutes, then gradually add the 250ml milk, stirring continuously, until a thick, smooth sauce forms. Season well, then stir in the mustard and parsley

Step 4

Pat the fish mix and prawns dry with kitchen paper, if needed. Add the fish mix, prawns and samphire to the sauce. Stir to combine, then transfer to a large oven dish (around 20x30cm) and set aside.

Step 5

For the topping, preheat the oven to 200ºC, gas mark 6. Pass the potatoes through a potato ricer into a large mixing bowl (or use a potato masher). Add the 50g butter, milk and ½ the capers and stir well until smooth and loose enough to spread easily. Season.

Step 6

Dollop the potato over the top of the fish mixture and spread right to the edges to cover and seal the filling underneath. Using the back of a spoon, swirl the potato, then sprinkle with the cheese. Toss the remaining capers in the oil, then scatter over the top.

Step 7

Bake for 25-30 minutes, until the topping is golden and the capers begin to crisp – the fish should be opaque and flake easily with a fork and the prawns should be pink, opaque and cooked through. Serve piping hot with green salad or freshly steamed vegetables, if liked.