1 Cutting board, 1 Small knife, 1 Measuring cups, 1 Pot, 1 Slotted spoon, 2 Ice cube trays, 1 Bowl, 1 Sieve, 1 Punch bowl, 1 Tablespoon
1 Put the potatoes in a large pan of salted water and simmer until tender. Heat the oven to 200ºC (180º fan) 400ºF, gas 6.
2 Meanwhile, place the fish in a large, wide pan and pour over the milk and fish stock. Add the thyme then bring to a boil and simmer very gently for about 5 minutes or until the fish just begins to flake. Remove the pan from the heat and strain the fish, reserving the cooking liquid, then break the fish into large chunks. Discard the fish skin.
3 Melt half the butter in a clean pan and gently cook the leek until soft but not brown. Add the flour and cook for 2 minutes, stirring all the time, then slowly add all but about 125 ml of the fish cooking liquid. Cook gently for 10 minutes then add the parsley and lemon zest, season with salt and pepper and carefully stir in the fish.
4 When the potatoes are cooked, drain them well, mash with the remaining butter and cooking liquid and season with salt and pepper. Pour the fish mixture into an ovenproof dish and spread the mashed potatoes on top using a palette knife. Bake in the oven for 15 minutes or until the potatoes are golden brown and the filling is bubbling.