Step 2

Meanwhile, put the milk in a large sauté pan, add the fish and bring to the boil. Remove from the heat, cover and stand for 3 minutes. Remove the fish, reserving the milk, then pat dry and gently flake into an ovenproof dish, discarding skin and bones.

Step 3

Heat the remaining olive oil in a pan, stir in the flour and cook for 30 seconds. Gradually stir in 200–250ml of the reserved milk. Grate in nutmeg, season, then bubble until thick. Stir in the cream.

Step 4

Preheat oven to 190C/fan 170C/gas 5. Add the grated artichokes, leek, prawns and herbs to the dish with the fish. Stir the lemon zest and juice into the sauce, then pour over. Mix gently.

Step 5

Spoon the mash over the fish mixture and use a fork to create peaks. Sprinkle over the Gruyère, then bake for 35–40 minutes until golden and bubbling. Serve with wilted greens.