Poach the fish in an open pan until just cooked and slightly translucent and sieve and retain the milk. Melt the butter take it off the heat and stir in the flour, this will be a very stiff paste. return to the heat and add the milk stirring all the time. You may need to add some fresh milk after the mixture has bubbled and thickened as you are aiming for a rich thick sauce, add a squeeze of lemon, nutmeg and season to taste, at this stage it should taste rich and creamy with just the slight tang of the lemon. Finally add the parsley.

Put the white fish salmon, prawns, peas and carrots in a dish. Pour over the sauce and incorporate but be careful not to break up the fish too much.

Finish with a layer of mashed potatoes on top, sprinkle on the cheese and bake in a high oven (410 F) until the sauce is bubbling up the sides and the peaks of the potato are turning brown.