Heat the smen or ghee in the base of a tagine or a large, heavy-based saucepan over a medium heat, stir in the onions, garlic, ginger and cumin seeds and cook for 2–3 minutes to let the flavours mingle. Add the cinnamon sticks, stir in the lamb and cook for a further 1–2 minutes.
Pour in the stock and bring to the boil, then reduce the heat, cover and cook gently for about 1 hour to cook the lamb and flavour the stock.
Add the chestnuts and honey, topping up the liquid if necessary to just cover the lamb and chestnuts. Re-cover and cook gently for a further 20–25 minutes until the chestnuts are tender.
Stir in most of the pomegranate seeds, season to taste and cook, covered, for 5 minutes. Garnish with the mint and coriander and the remaining pomegranate seeds. Serve with couscous, if liked.