Heat the smen or ghee in the base of a tagine or a large, heavy-based saucepan over a medium heat, stir in the onion, garlic and sugar and cook for 2–3 minutes to soften a little. Add in the lentils, stir to coat well, then stir in the ras el hanout.
Pour in the measurement water, bring to the boil, then reduce the heat, cover and cook gently for about 35 minutes until the lentils are tender but not mushy. Season well with salt and pepper and garnish with the coriander. Serve as a side dish or as a snack with a dollop of yogurt and toasted flat breads, if liked.