Preheat the oven to 200C/180C Fan/Gas 6.
Butter a large ovenproof dish.
Put the potatoes into salted water in a large saucepan.
Boil for around 4 minutes.
Add the cauliflower and broccoli to the pot.
Boil for another 4 minutes.
Drain well and add vegetable mix into the prepared ovenproof dish.
Season with salt & pepper.
Put the cornflour into a bowl.
Add cream and spring onions.
Whisk to combine.
Scatter half the cheese over the vegetable mix. Scatter over the chopped parsley.
Top the mixture with the haddock.
Pour the cream mixture over the top.
Scatter over the remaining cheese.
Bake for 20–25 minutes, until golden-brown.
Add more chopped parsley if you wish.