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 and garlic with the coriander, cumin and fennel seeds and cook for 2–3 minutes to let the flavours mingle. Add the chickpeas, stir to coat well and cook for a further 1 minute, then add the chestnuts and ras el hanout.
Stir in the tomatoes and sugar and add enough water to just cover the chickpeas and chestnuts. Bring to the boil, then reduce the heat, cover and cook gently for 25–30 minutes. Season to taste with salt and pepper, then stir in most of the parsley. Garnish with the remaining parsley and serve with chunks of fresh crusty bread, if liked.