Gently poach some salmon, cod and smoked haddock in milk, seasoned with a few black peppercorns and a bay leaf, until just cooked – about 5 minutes.
Drain and flake the fish into large chunks, removing any skin and bones. Place the fish in a casserole dish. Strain the poaching milk.
Melt a couple of Tbs of butter in a saucepan and add 2 Tbs plain flour, stirring over a gentle heat to cook the flour, then add the milk
slowly while stirring all the while, to make a nice thick sauce. You could also add a handful of grated cheddar and some chopped parsley.
Pour this over the fish and leave to cool. Boil potatoes until soft, then mash with a good knob of butter. Spread the potato over the fish
and sauce, ensuring it’s all covered right to the edges, forking up the top to roughen the surface, then sprinkle over some grated cheddar if you wish.
Bake for about 30 minutes in a 180° oven, until crisp and golden on top, and serve with something green.