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.
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.
Strain the infused milk through a sieve
into a large shallow sauté 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.
Stir the slackened cornflour, then stir
it into the hot milk in the sauté 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.
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.