Scrape one small carrot and pare one small turnip, removing a thick skin. Grate and add them to one cup of soup stock and let it simmer 45 minutes. Pare one potato, cut it into small cubes and add it to the stock after the turnip and carrot have cooked 15 minutes. Add some tomato, if desired. The soup may be varied by using rice or noodles with the stock, instead of vegetables.