Tip the couscous into an ovenproof dish. Stir the 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. Scatter over the butter and cover with a damp piece of greaseproof paper. Place in a preheated oven, 180°C (350°F), Gas Mark 4, for about 15–20 minutes until heated through.
Meanwhile, heat the smen or ghee in the base of a tagine or a heavy-based frying pan over a medium heat, stir in the onions, ginger and cinnamon sticks and cook for 3–4 minutes to flavour the smen. Add the sultanas or raisins, saffron water and honey, then cover and cook gently for 10 minutes. Season with salt and pepper.
Pile the couscous in a conical mound on a shallow serving dish and use a spoon to create a hollow in the top. Spoon the tfaia into the hollow and around the base of the couscous and garnish with the coriander. Serve as an accompaniment with tagines or grilled dishes.