1. Soak beans in 2 1/2 pints water overnight. Next day, transfer beans and water to a saucepan, add salt and cook for 1 hour.
2. Melt dripping in a flameproof casserole and brown chops well on all sides. Peel and chop onion and add to casserole. Cook till transparent. Add beans and water, tomato puree, cumin, bay leaf, rosemary and garlic salt. Cover and cook for 1 hour.
3. Uncover and cook for a further 20 minutes till meat is tender.
4. Just before serving, stir in a pinch of sugar and the vinegar and sprinkle with chopped chives.