Heat the oven to Gas Mark 6, 180ºC fan, 200ºC.
Lightly rub the aubergines with oil and place on a baking tray. Bake for 20 minutes, turning once.
Heat the remaining oil in a large, heavy-based casserole dish or tagine. Add the onion and saute for 2-3 minutes. Add the chicken to the dish, reduce the heat and cook for 10 minutes, until lightly browned. Stir in the harissa and tomato puree.
Pour in 400ml (14fl oz) of the stock and bring to a simmer. Remove the stalk from the cooked aubergines and cut them into chunks. Add to the chicken, cover and simmer for 20-25 minutes, until the chicken thighs are cooked through and juices run clear.
Mix a little of the casserole liquid into the cornflour then stir back into the chicken to thicken. In a separate dish pour the remaining stock over the couscous and stir in the coriander. Spoon the couscous over the chicken and return the lid. Turn off the heat for 5 minutes until the couscous is cooked.
Fluff the couscous with a fork before serving.
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