Cooking classic fish pie with local catch

A dish shaped by the tide

There is a particular sort of evening on the British coast when the light goes grey over the harbour wall, the wind picks up off the water, and the windows of the pubs along the quay start to glow. That is fish pie weather. Not the weather for something delicate and plated with tweezers, but for a deep dish of flaked fish under a golden, buttery mash that you eat with a spoon and a slice of bread.

Fish pie suits coastal living because it is generous rather than precise. It makes sense of a mixed bag of fillets, it stretches a modest amount of expensive fish further than almost anything else, and it improves overnight. Buy well and cook it plainly, and it will taste of the sea rather than of sauce.

Buy where the boats come in

If you live near a harbour, use it. A fishmonger who unloads at the same quay each morning will tell you what is worth buying today, and that advice is worth more than any recipe note. Ask what was landed, ask what is firm, and ask what they would take home themselves.

Look for fish with bright eyes, translucent flesh and a clean, sea-smelling freshness. Fillets should feel springy, not sloppy. If the catch is thin that week, frozen-at-sea fillets are a perfectly good substitute; they are frozen within hours of landing and often better than tired fresh fish that has travelled. A good fishmonger will also skin and pin-bone for you, which saves a fiddly job at home.

What you need before you start

Serves four generously, or six with plenty of greens alongside.

• For the filling: 400g firm white fish — haddock, cod, coley or pollack — cut into large chunks
• 200g smoked haddock, un-dyed if you can get it, plus 150g salmon or a handful of peeled prawns if you like
• 500ml whole milk, 1 bay leaf, 6 black peppercorns, a strip of lemon zest
• 50g butter and 50g plain flour for the roux
• 2 tbsp double cream, 1 tsp Dijon mustard, 1 tbsp capers, a squeeze of lemon juice
• A small bunch each of flat-leaf parsley and dill, chopped
• 2 hard-boiled eggs, quartered (optional, but very traditional)
• For the topping: 1.2kg floury potatoes such as Maris Piper or King Edward
• 75g butter, 100ml warm milk or cream, 1 egg yolk, 50g mature cheddar or Gruyère, grated

The filling: poach gently, thicken properly

Put the milk in a wide pan with the bay leaf, peppercorns and lemon zest and bring it just to the edge of a simmer. Add the fish in a single layer, cover, and poach for five or six minutes, until the flesh turns opaque but still gives slightly when pressed. Do not let it boil, or the fish will tighten and turn cottony. Lift the fish out with a slotted spoon and strain the milk, keeping every drop.

Melt the butter in a clean pan, stir in the flour and cook for two minutes without colouring. Add the reserved milk gradually, whisking as you go, then simmer for three or four minutes until the sauce coats the back of a spoon. Stir in the cream, mustard, lemon juice, a good pinch of salt and plenty of white pepper. It should be thick enough to hold, because the fish releases liquid in the oven.

Flake the fish into large chunks — you want to see pieces, not paste — and fold it gently into the sauce with the herbs, capers and eggs. Tip into a buttered dish about 20cm by 28cm, spreading it level but not pressing it down. Chill while you make the mash, which also helps the filling set.

The mash: dry, buttery, ridged

Peel and cut the potatoes into even chunks, then boil them in well-salted water until a knife slides through easily. Drain thoroughly and return them to the hot pan for a minute to steam dry. This step matters more than any other: wet mash will sink into the filling and turn the whole thing soupy.

Mash or rice the potatoes, then beat in the butter first, followed by the warm milk, the egg yolk and a generous grating of nutmeg. Taste and season again. The mash should be soft enough to spread but firm enough to hold a ridge.

Spoon it over the cooled filling and spread it to the edges, sealing right against the dish so no sauce escapes. Run a fork across the surface in wavy lines and scatter over the cheese. Those ridges catch the heat and turn crisp and golden.

Into the oven, then onto the table

Bake at 200°C (180°C fan, gas mark 6) for 30 to 35 minutes, standing the dish on a baking tray to catch any bubbling over. It is ready when the sauce is visible and restless at the edges and the top is deeply golden. If the mash browns faster than the middle heats through, cover loosely with foil.

Rest it for ten minutes before serving, which lets the filling firm up enough to spoon out cleanly. Buttered greens, peas or a sharp watercress salad cut through the richness; a glass of dry white or a light ale does the same job.

Any leftovers reheat well the next day, though you may want a splash of milk to loosen the sauce. Better still, make two and freeze one before baking — then on the next squally harbour evening, dinner is already made.