Ballymaloe Irish stew

STOCK: Place bones, herbs, vegetable peelings and trimmings in a saucepan and add enough cold water to cover by 5 cm. Bring to boil, reduce heat and simmer, partially covered, for about 2 hours.
Strain and skim off fat. Reserve 625 ml (2 1/2 cups) stock. Chop mutton or lamb fat into small pieces, if using, and fry over moderately low heat in a heavy-based frying pan until fat renders.
Reserve 45 ml (3 tbsp) of rendered fat (dripping), pour into a heavy-based saucepan and brown chops on both sides, in batches. Add carrots, onions, salt, pepper and 600 ml (2 3/5 cups) reserved stock. Place potatoes on top.
Simmer stew gently, covered, for 1 1/2-2 hours, or until meat is tender. Transfer meat and vegetables to individual bowls with a slotted spoon. Skim fat from stock. Taste and adjust seasoning.
Swirl in butter, parsley and chives and ladle sauce over meat and vegetables.