Put water on to boil. Peel and chop the onion. Heat the butter and olive oil in a large, heavy frypan. Add the onion and fry gently until soft.
Meanwhile, peel the carrots, swede and parsnip. Cut into 1cm chunks and add to the onions. Stir in the cayenne, turmeric, ginger, cinnamon and the saffron threads, if using, and season to taste with salt and black pepper.
Chop the apricots and add them, along with the baby peas. Drain, rinse and add the chick peas. Add 300ml boiling water and bring back to the boil. Reduce the heat, cover and simmer for 15 minutes.
Meanwhile, pour 1 cup boiling water into a saucepan, add the couscous and stir, then leave to stand, covered, until the vegetables are ready.
When the vegetables are cooked, season the couscous to taste with salt and pepper. Break up with a fork and transfer to a serving dish. Spoon the vegetables over the top, garnish with coriander and serve.