Low-cal, low-fat and economical to boot! Boiling the bone with the beans and vegetables gives the broth major ham flavor.
Rinse dried beans. In a large pot, combine beans and 8 cups water. Bring to boiling; reduce heat. Simmer, uncovered, for 2 minutes. Remove from heat. Cover and let stand for 1 hour. (Or place beans in water in pot. Let soak, covered, in a cool place for 6 to 8 hours or overnight.) Drain and rinse beans; set aside.
In the same pot, brown ham bone on all sides in hot butter over medium heat. Stir in soaked beans, salt, pepper and 8 cups fresh water. Bring to boiling; reduce heat. Simmer, covered, for 1 to 1-1/2 hours or until beans are tender, adding fennel, carrot and green beans for the last 30 minutes of cooking.
When beans and vegetables are tender, remove ham bone. When cool enough to handle, cut meat off bones. Coarsely chop meat and return to soup pot, along with the oregano; heat through. Remove from heat. Stir in vinegar just before serving.