If you have a pork-bone from the fresh meat, let it boil in water for an hour. Put the pan to cool and take off the fat, and remove the bone. Replace the pan on the fire and throw into it two pounds of Brussels sprouts. Do not add onions to this soup but leeks, and the hearts of cabbage. Pepper and spice to taste. Rub it through a sieve and let it be thick enough to form a thin purÉe.