Tip the couscous into a heatproof bowl. Stir half a teaspoon of salt into the measurement water and pour over the couscous. Stir once to make sure all the grains are submerged in the water, then cover with a clean tea towel and leave to stand for 10–15 minutes. Rake a fork through the couscous to break up the grains. Then, using your fingers, rub the oil into the grains until light, airy and any lumps are broken up.
Melt the smen or ghee in a heavy-based frying pan over a medium heat, stir in the cardamom seeds and cook for 1 minute. Add the dates and cook for 1–2 minutes, then stir in the ras el hanout. Add the couscous and stir well, making sure it is thoroughly mixed and heated through. Season with salt and pepper and toss in most of the coriander.
Pile the couscous in a mound on a shallow serving dish, garnish with the remaining coriander and serve with dollops of yogurt.