Preheat the oven to 140°C.
Place onions, tomatoes, chives, mint, and oregano in a roasting tin, top with lamb, and add oil and wine.
Cover tightly with foil and cook for 3-4 hours until the meat is very tender.
Boil potatoes and celeriac in salted water for 15-20 minutes until tender.
Drain and mash the vegetables with butter, cheese, cream, and nutmeg until smooth.
Preheat the oven to 180°C.
Blend the roasting tin contents into a purée to create a sauce after removing large herb stalks.
Brush the lamb with a honey and thyme mixture.
Cut lamb into bite-sized pieces and roast at 180°C for 10 minutes until golden.
Serve the lamb over a scoop of warm mash and drizzle with the reheated sauce.