Healthy fish pie with prawns and leeks

1 Put the potatoes in a large pan of cold water and bring to the boil. Reduce the heat, cover, then simmer for 15 min or until soft. Drain, then return to the pan over a low heat for 30 sec to dry off any excess moisture. Mash with 1 tablespoon olive oil, then season with ground black pepper.

2 Meanwhile, put the milk in a large frying pan, add the fish and bring to the boil. Remove from the heat, cover and stand for 3 min. Remove the fish (reserving the milk) and pat dry with kitchen paper, then gently flake into an ovenproof dish, discarding the skin and any bones.

3 Heat the remaining oil in a saucepan, then stir in the flour and cook for 30 sec. Gradually add 3/4 to 1 cup of the reserved milk (discard the rest). Add the nutmeg and some black pepper and simmer until thick.

4 Preheat the oven to 190°C/fan 170°C/gas 5. Grate the artichokes and add to the fish with the leek, prawns and herbs. Stir the lemon zest and juice into the white sauce, then pour over. Mix gently.

5 Spoon the mash on to the fish mixture, then use a fork to make peaks. Sprinkle over the grated cheese, then bake for 35–40 min until golden and bubbling.