In 6 quart kettle, slowly brown ox tails in butter, about 1/2 hour. Add 3 quarts water and bring slowly to a boil. Skim foam from surface several times. Add salt, onions, parsley sprigs, thyme, peppercorns and bay leaf. Bring to a boil. Simmer low heat, covered for 3 hours. Remove from heat. Remove ox tails and cut meat off bones. Next cut carrots and turnips (or cabbage) into strips 2" long. Cut celery in 2" pieces and in half lengthwise. Add meat, carrots, turnips and celery. Bring to a boil. Simmer until vegetables are done (tender crisp 5 minutes). Add sherry; simmer 5 more minutes. Garnish with parsley.