Serves 4

50g unsalted butter
50g plain flour
125ml white wine
500ml fish stock
90ml double cream
Juice of half a lemon
1 tbsp english mustard
1 tsp worcestershire sauce
½ tsp anchovy essence
Salt and pepper
200g boneless cod fillet, skinned and cut into rough 3cm chunks
200g salmon fillet, skinned and cut into rough 3cm chunks
200g smoked haddock fillet, skinned and cut into rough 3cm chunks
Half a small bunch flat-leaf parsley, chopped

For the topping

50g unsalted butter
50ml milk
1kg floury potatoes, peeled, cooked and dry-mashed

1 To make the sauce, melt the butter in a heavy-bottomed saucepan over a low heat and gently stir in the flour. Gradually add the wine, stirring well. Slowly add the fish stock (a good quality cube is fine) until you have a silky smooth sauce. Bring to the boil and simmer quietly for 15 minutes. To finish, add the cream and lemon and briefly bring to the boil again. Stir in the mustard, worcestershire sauce and anchovy essence. Season.

2 Gently fold the fish and parsley into the hot sauce, and pour into a large pie dish up to about 3cm from the top of the dish. Leave to cool, so the topping will sit on the sauce when piped.

3 Mix the butter and milk into the mashed potato until soft enough to spread over the fish mixture. Season. Pipe or gently fork to cover the fish.

4 Preheat the oven to 190C/Gas 5 and bake for 30-40 minutes until bubbling and golden.