After you have boiled a cauliflower, it is a great extravagance to throw away the liquor; it is delicately flavored and forms the basis of a good soup. Wash well your cauliflower, taking great care to remove all grit and insects. Place it to simmer with its head downwards, in salted water; and, when it is tender, remove it. Now for the soup. Let all the outer leaves and odd bits simmer well, then pass them through a sieve. Fry some chopped onions, add the liquor of the cauliflower and the pieces that have been rubbed through the sieve, add a little white pepper and a slice of brown bread. Let all cook gently for half-an-hour, then, just before serving it, take out the slice of bread and sprinkle in two teaspoonfuls of grated Gruyere cheese.