Put the pork into a soup pan, cover it with plenty of cold water and bring slowly to the boil. Skim, then add the vegetables, cover and simmer gently for 2 hours.
Meanwhile prepare the poule verte. Briefly blanch and then refresh the cabbage leaves. Drain them and spread out flat on a board. Chop up the ham and belly of pork together with the onion and garlic. Bind these with the