Chop all ingredients. Saute mushrooms and onions 5 minutes in butter. Stir in bread crumbs and crabmeat.Cook 2 minutes. Add salt, pepper, lemon juice, and ketchup. Pour in cream half and 0.5. Put in flounder. Bake 220ÂșC or 10-15 minutes/ Pat of butter on top and serve with mornaise sauce.