A Dish Built for Chilly Coastal Evenings

There is a particular kind of evening on the British coast — the sort where the light goes early, the wind comes off the water with a bite, and the windows of the pubs along the front start to glow amber. That is fisherman's pie weather. Not a fish pie with a pastry lid, and not quite a gratin either: it is smoked haddock and prawns folded through a gentle white sauce, capped with buttery mash and baked until the top bronzes and the edges bubble.

It is also one of the most forgiving dishes you can make at home. The filling can be prepared in advance, the mash is plain comfort, and the whole thing comes out of the oven looking as though you have been at it all afternoon. Here is how to do it properly, with the sort of detail that makes the difference between a good pie and a memorable one.

Choosing Your Fish and Prawns

For four generous portions you want roughly 400g of undyed smoked haddock and 200g of raw king prawns. Undyed matters: the yellow stuff is a dye, and it adds nothing but colour. If your fishmonger only has dyed, it will still taste fine — just don't expect a snowy white sauce.

• Smoked haddock: ask for a thick fillet from the middle of the fish, and have it skinned and pin-boned. Cut it into rough 4cm chunks at home.
• Prawns: raw, peeled, and thoroughly dried on kitchen paper. Cooked prawns will turn to rubber in the oven, so don't be tempted.
• Economy: a handful of cold-water prawns stirred in at the last moment is a thrifty way to bulk things out without losing flavour.
• Freshness: firm flesh, a clean sea smell, no trace of ammonia. If the fish smells sharp, walk away.

If smoked haddock is hard to source, smoked cod or smoked pollock works well. Avoid anything heavily dyed or oversalted, and taste before you season the sauce.

The Creamy Base That Holds It All Together

Start by infusing 500ml of whole milk. Warm it gently in a pan with a bay leaf, a few black peppercorns, a strip of lemon zest and half an onion studded with two cloves. Bring it just to the edge of a simmer, then take it off the heat and leave it to steep for ten minutes. Strain it into a jug.

In a heavy pan, melt 50g of butter, stir in 50g of plain flour and cook the roux over a low heat for two minutes — long enough to lose the raw flour taste, not long enough to colour it. Add the warm milk a ladleful at a time, whisking smooth between each addition. The sauce should be thick enough to coat the back of a spoon, because the fish will release liquid as it bakes.

Off the heat, stir in a teaspoon of Dijon mustard, two tablespoons of double cream, 60g of grated mature cheddar, a good grating of nutmeg and plenty of white pepper. Go easy on the salt. Fold through the raw haddock and prawns, plus a handful of chopped flat-leaf parsley and, if you like the classic touch, two hard-boiled eggs cut into quarters. Let the filling cool while you deal with the potatoes.

The Mash Topping That Holds Its Own

Use 1kg of floury potatoes — Maris Piper, King Edward or Rooster. Peel and cut them into even chunks, then start them in cold salted water and boil for fifteen to eighteen minutes, until a knife slides in without resistance.

Drain thoroughly, return the pan to a low heat for a minute to drive off excess steam, then mash or pass the potatoes through a ricer. Add 60g of butter, 100ml of warm milk, one egg yolk and a little grated nutmeg, and beat until smooth but not gluey. Overworking floury potatoes makes them sticky.

The mash should be soft enough to spread easily but sturdy enough to hold a ridge. It has to sit on top of a wet filling for half an hour without sinking into it, and that firmness is exactly what you want.

Assembling and Baking

Use a shallow ovenproof dish of about 1.5 to 2 litres. A deep narrow dish means too little topping for the amount of filling; a wide shallow one gives you that all-important ratio of crust to sauce.

• Pour the filling in and level the surface, then leave it to settle for ten minutes.
• Spoon the mash over in blobs, then spread it gently with a fork or palette knife so it seals right to the edges.
• Rough up the surface with the tines of a fork. Those ridges are where the browning happens.
• Scatter over the remaining cheddar and dot with a little butter.
• Bake at 200°C (180°C fan, gas mark 6) for 25 to 30 minutes, until the top is golden and the sauce bubbles up around the sides.

If the top catches before the middle is hot, cover loosely with foil. When it comes out, rest it for ten minutes. This is not optional — it lets the sauce set slightly so it doesn't flood the plate on serving.

Serving, Making Ahead and Variations

Serve with buttered peas, spring greens or a sharp watercress salad to cut through the richness, and good crusty bread to mop up. A dry white wine works, but so does a strong cup of tea on a cold night.

To make ahead, assemble the pie, cool it completely and refrigerate for up to 24 hours, then bake from cold, adding 10 to 15 minutes. It freezes well before baking for up to a month — defrost overnight in the fridge first. Leftovers reheat covered at 180°C with a splash of milk.

Once you have the method, play with it: sweated leeks in the sauce, a spoonful of horseradish in the mash, a handful of mussels, or Gruyère instead of cheddar. It is that sort of dish.