This is the perfect winter comfort food. You can use whatever fish you like here. I like to use mainly pollack, adding squid, scallops and a few North Atlantic prawns for flavour, but some smoked fish (traditionally haddock) will add a good flavour too.
1kg mixed fish
800ml full-fat milk
1 bay leaf
about 6 black peppercorns
medium bunch parsley, leaves picked and chopped, stalks reserved
50g flour (‘00’ if you have it)
75ml single cream
1 heaped tablespoon dill, finely chopped
3 heaped tablespoons cornichons, drained and roughly chopped
2 tablespoons capers, rinsed and drained
juice of ½ lemon
1.2kg floury potatoes
1 egg white (optional)
salt and pepper
Preheat the oven to 200°C/gas 6. Put the fish (apart from any squid or scallops) into a large shallow dish – the one you intend to make the pie in is fine. Cover with the milk, and add the bay leaf, peppercorns and the stalks of the parsley. Bake in the oven for 10 minutes, to lightly poach the fish.
Remove the fish from the oven and drain off the milk, reserving it for later. Pick out any bones you can see, along with the bay leaf and peppercorns, and break up the fish roughly. Cover to prevent it stinking out the kitchen and set aside.
In a large saucepan, melt 75g of the butter and add the flour, stirring over a low heat for several minutes until it turns golden and sandy. Gradually add most of the fishy milk, stirring all the while so that it becomes a smooth sauce – keep back 50–100ml of the milk to use for the mash. When the sauce is thick enough to coat the back of a wooden spoon, stir in the cream and cook on for a few minutes.
Remove the pan from the heat and stir in the chopped parsley, dill, cornichons, capers and lemon juice, then be brave with the salt and pepper. Pour the sauce over the cooked fish and mix well. It should be quite saucy and runny but will thicken up on further baking. Allow it to cool a bit before scattering over any scallops, squid or prawns you are using.
Peel, halve and boil the potatoes in a large pan of water for 25–30 minutes, or until tender. Drain well, return the cooked potatoes to the pan and crush roughly with a potato masher.
Bring the remaining milk back to the boil and add the last of the butter, a good quantity of salt and pepper, and the egg white if you are including one. Mash very well (or beat with an electric whisk), until it is as smooth and fluffy as possible. Set aside to cool.
Spread the mash over the fish mixture. Scrape ridges along the surface with the tines of a fork, and season again. At this point you can leave it in the fridge for a day, or freeze it to use in the future. When you’re ready to cook, preheat the oven to 200°C/gas 6 and bake for 45 minutes, until the top is turning golden and the sides are bubbling up.
Joanna Weinberg has written cookery columns for The Times, Red and currently Conde Nast Traveller. She runs Kitchen Table Cookery School at The Talbot Inn, Mells, Somerset