Cut up and boil potatoes in salted water until tender, drain, add milk and butter and mash to a smooth consistency, set aside.
Steam broccoli, carrots and corn until tender and set aside.
Poach fish in milk until cooked through, set fish aside and reserve milk.
To make sauce, make a roux by melting butter in a saucepan, adding flour and mix until well combined, next add the reserved milk a little at a time whisking non stop until all milk is used and well combined. Add chopped parsley and simmer until required consistency is achieved, which should be slightly thick but not gloopy. you can add wine here if using.
Put fish into a large oven proof dish and chopinto bite size pieces. Season with salt and pepper. next add vegetables, pour over sauce and top with mashed potatoes. Run the fork over the top of the potatoes to slightly flatten and achieve fork grooves. Finally sprinkle on cheese and place under the broiler until the cheese has melted and the pie warmed through, the longer you leave the crunchier the topping will be. serve with a selection of vegetables if required such as peas.