Take half a dozen young turnips, cut them in quarters, cook them a little while in a saucepan with butter, and remove from the fire before they are browned. Add a good deal of salt (this soup requires more salt than other vegetable soups), a pinch of sugar, a good piece of butter; fill the saucepan with boiling water, bring to the boil and let it simmer for four hours. Squash the turnips through a fine sieve and add, little by little, some of the stock to the purée so that the soup is sufficiently thick. Serve with croûtons. You can also, just before serving, add a liaison of cream and yolk of egg.