Directions

1. Mix 3 tbsp of the milk into the cornflour and set aside. Pour the rest of the milk into a saucepan. Shell the prawns, reserve the meat, then drop the shells and heads (wash them first if necessary) into the milk along with the thyme sprigs, bay leaves, garlic and a grind of pepper. Bring to a boil, then remove from the heat and leave to infuse for 20 mins.
2. Meanwhile, put the potatoes into a large pan of water, bring to the boil and simmer for 20 mins until tender. Drain. Steam the sliced leek for 3 mins, then remove from the heat and set aside.
3. Strain the infused milk through a sieve into a large shallow saute pan. Lay all the fish fillets (not the prawns) in the milk. Bring to a boil, then lower the heat and simmer gently for 3 mins. Remove from the heat and leave, covered, for 5 mins. Use a slotted spoon to transfer all the fish to a dish and leave to cool slightly. Heat oven to 200C/180C fan/gas 6.
4. Stir the slackened cornflour, then stir it into the hot milk in the saute pan. Return the pan to the heat and stir until thickened. Briefly stir in the soft cheese, remove from the heat, then add the parsley and season with black pepper. Stir in any liquid that has drained from the fish. Break the fish into big pieces as you lay them in a 2-litre ovenproof dish so that the different varieties are evenly distributed. Scatter over the prawns and leek, then season with pepper. Pour the sauce over and give a few gentle stirs to evenly distribute the sauce and combine everything without breaking up the fish.
5. Using a large fork, crush the potatoes by breaking them up (not mashing them) into chunky pieces. Mix in the oil, chives and a grind of black pepper. Spoon the potato crush over the fish. Sit the dish on a baking sheet and bake for 25-30 mins, or until the sauce is bubbling and the potatoes golden. Alternatively, make the dish completely, refrigerate it for several hrs or overnight, then bake at the same temperature as above for 45 mins.