1kg (2lb 4oz) white floury potatoes, such as Desirée or Maris Piper
1 large onion, thinly sliced
4–6 garlic cloves, peeled and thinly sliced
2 tablespoons chopped marjoram, plus a couple of marjoram flower stems for topping (optional)
500ml (17fl oz) double cream
300–400g (101⁄2–14oz) thoroughly soaked salted pollack or cod fillets, skinned and sliced into small pieces
salt and freshly ground black pepper
Heat the oven to 160°C/315°C/gas mark 2–3.
Peel and slice the potatoes thinly into 2–3mm (3⁄4–11⁄4in) rounds. Place the slices in a large bowl with the onions, garlic and marjoram, and plenty of black pepper (it may not need salt as the fish will bring this to the mix). Place the cream into a small pan over a medium heat and bring it up to a simmer. Pour the hot cream over the potatoes and turn well to combine.
Place a relatively neat layer of overlapping potatoes in the bottom of a large round dish about 20–25cm (8–10in) in diameter and 5cm (2in) deep. Scatter over some of the sliced fish, then make a second layer of overlapping potatoes. Continue until you have used up the fish, finishing with a layer of potato on top. Pour over all the remaining cream from the bowl. Top with a couple of marjoram flower stems, which I think look lovely and dry brittle as glass in the oven – but of course they’re not essential.
Place the dish in the oven and bake the layered potato-and-fish pie for 1 hour, pressing the potatoes down firmly once or twice during cooking using a spatula, until the potatoes are tender, the top layer is golden and the sauce is bubbling. Remove the dish from the oven and allow it time to settle. It will be much better, and still nice and hot, after 30 minutes of sitting. Serve with a green salad or steamed, lemony purple-sprouting broccoli.