Chop approximately 800g skinned and filleted white fish into bite sized pieces and scatter into a dish.
Sauté 3 finely chopped shallots in butter until soft. Add about 285ml double cream, a bay leaf and a splash of vermouth or white wine then bring to the boil and simmer gently for about five minutes. Turn off the heat and remove the bay leaf. Stir in the juice of half a lemon, a handful of chopped parsley and some grated hard cheese to taste. Season then pour over the fish.
Top with buttery mashed potato and bake at 200c for 30-40 minutes until golden.