Chop and peel potatoes same length and boil

Add the fish to a pan that will fit all the fish in a single layer, scatter over the onion. Pour over 500g of milk and dot to the surface with 25g butter and season with salt and pepper. Bring to steady simmer and cover with a lid.

Add the fish to a baking dish and evenly scatter over the prawns.

In a clean sauce pan melt 50g butter, then stir through flour to form a roux. Allow to cook over a gentle heat for a couple of minutes before pouring over the pouching milk, onions and all..... Whisk constantly over a medium heat for about 5 minutes until sauce is thick and smooth, add your nutmeg - season, stir through the parsley and pour the sauce over the fish spreading evenly.

Using a fork spread the mash over the oven dish. Sprinkle on the cheese for 30 min until golden and crispy (gas mark 6)