1. Make 800ml stock with lamb bones and trimmings from the carrots and onions and some fresh parsley stalks.
2. Cut the lamb into large chunks and put in a heavy-based pan. Pour in the stock and bring to the boil, skimming frequently.
3. Remove the lamb with a draining spoon and reserve. Strain the stock into a clean pan. Add the lamb and bring back to the boil, reduce the heat, cover and simmer gently for 10 minutes.
3. Meanwhile, cut the carrots and potatoes into chunks. Add carrots, onion and floury potatoes to the pan and simmer for another 10 minutes. Add the waxy potatoes and the thyme and simmer a further 1520 minutes or until the lamb is very tender. The floury potatoes will have broken down to thicken the sauce, while the waxy potatoes will keep their shape.
4. Remove from the heat, cover and leave, without stirring for 15 minutes. Check seasoning, serve generously sprinkled with fresh chives and parsley.