Fish is boiled in 250 ml water, 250 ml milk, a little pepper and salt. While hot cleanse the skin and bones. Cut the mushrooms, sprinkle with lemon juice and sauté in 1 tbsp butter. Make a sauce from the remaining milk, flour and broth in which fish is boiling. Ranks in a fireproof container line fish line mushrooms, fish again, pour the sauce, sprinkle with plenty of grated cheese and a little bread crumbs, put a few pieces of butter on top and bake until crust catch.