Line bottom and sides of dish with potatoes. Lay half the sausages (cut breakfast sausages in half) on top, then onion rings, cover with half tin tomatoes. Season with pepper. Place another layer of potato slices, sausages and onion rings over this and add ramaining tomatoes and season once again with pepper. Cover with a thin layer of potatoe slices, dot with butter and place in oven.
Cook until potato topping is well browned and rest have all but dissolved.