Purée of Carrot Soup

Procedure

1. Heat the butter in a heavy saucepot over moderately low heat.
2. Add the carrots and onions, and sweat the vegetables until they are about half cooked. Do not let them brown.
3. Add the stock and potatoes. Bring to a boil.
4. Simmer until the vegetables are tender.
5. Purée the soup by passing it through a food mill or by u