The restaurant J Sheekey in London started as an oyster bar in 1896. This is one of its most famous dishes

Serves 2

250ml fish stock (a good-quality cube will do)
50ml white wine
125g boneless cod or haddock fillet, skinned and cut into rough 3cm chunks
125g boneless salmon fillet, skinned and cut into rough 3cm chunks
1 tbs chopped parsley

for the sauce:
25g butter
25g flour
90ml double cream
1 tsp English mustard
1 tsp Worcestershire sauce
½ tsp anchovy essence
salt and freshly ground black pepper

for the topping:
20-30g butter
500g floury potatoes, peeled, cooked and mashed
salt and freshly ground white pepper
1 tbs milk
15g fresh white breadcrumbs
10g grated Parmesan

In a large pan, bring the fish stock and white wine to a simmer and poach the fish gently in the liquid for 2 minutes. Drain in a colander over a bowl and leave to cool.

To make the sauce, melt the butter in a thick-bottomed pan over a low heat, then stir in the flour. Gradually add the drained stock and wine mixture, stirring well until it has all been added. Bring to the boil and simmer gently for 30 minutes. Add the double cream and continue to simmer for 10 minutes or so, until the sauce has a thick-coating consistency. Stir in the mustard, Worcestershire sauce and anchovy essence, and season with salt and freshly ground black pepper if necessary. Leave to cool for about 15 minutes.

Gently fold the cooked fish and the parsley into the sauce, and spoon into 2 individual pie dishes or 1 large one, to about 3cm from the top of the dish. Leave to set for about 30 minutes, so that the topping will sit on the sauce when piped over it.

Mix the butter into the mashed potato, season with a little salt and freshly ground white pepper, and add a little milk so that the mixture is soft enough to pipe. Using a piping bag, pipe the potato over the pies in whatever pattern you feel comfortable with.

Preheat the oven to 180C/gas 4 and bake for 30 minutes, then scatter on the breadcrumbs and cheese, and bake for a further 15 minutes until golden.

• This recipe is taken from Cook: a year in the kitchen with Britain’s favourite chefs by Rebecca Seal (£25, Guardian Books, or £17.50 from the Guardian bookshop)

Life and style | guardian.co.uk