1. Rinse beans. In a large pot, combine beans and 8 cups water. Cover and let stand in a cool place for 6 to 8 hours or overnight. (Or for a quick soak method, bring beans to boiling; reduce heat. Simmer, uncovered, for 2 minutes. Remove from heat. Cover and let stand for 60 minutes.) Drain and rinse beans; set aside.
2. In the same pot, add ham bone and remaining 12 cups water. Bring to boiling; reduce heat. Simmer, uncovered, for 1 hour. Add beans and thyme to the pot. Simmer, uncovered, for 40 minutes.
3. Add onion, carrots, celery and salt to pot. Simmer, uncovered, for 30 minutes or until beans and vegetables are tender and ham is falling off the bone.
4. Remove ham bone from pot. When cool enough to handle, cut meat off bone; coarsely chop. Discard bone. Using a potato masher, slightly mash beans and vegetables in pot. Stir in chopped ham; simmer mixture for 10 minutes more. Season to taste with additional salt and black pepper. If desired, garnish each serving with parsley.

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*Note: Purchase a 9- to 10-pound bone-in, smoked fully cooked ham and cut a 3½ -pound portion that includes the bone to use in the soup. Reserve remaining ham for another use.

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