Three potatoes, one and one-half cups water, three cups milk, one onion, three teaspoonfuls salt, one and one-half tablespoonfuls flour, one and one-half tablespoonfuls butter. Boil potatoes until soft, drain and mash them. Cook the onions in the milk ; add this to the mashed potatoes, add the salt and pepper. Melt the butter in a pan, add flour, add this to the soup, let boil up once, strain and serve hot.