Clean, wash and chop the beans. Cook in 1/2 litre boiling salted water for about 7 minutes. Drain and collect the cooking water. Fill up the cooking water with broth. Peel, wash and cut potatoes into large cubes. Peel and chop onion. Fry potatoes and onion in hot oil.
Pour on stock and cook for about 15 minutes. Puree, stir in cream. Add beans. Pluck the marjoram leaves from the stalks. Season soup with salt, pepper and marjoram. Cut ham into cubes. Ham and sprinkle over the soup just before serving