Wash and pick over the mushrooms carefully. Cover with half the stock and leave to soak for about 15 minutes.
Heat one-third of the butter with the oil in a flameproof casserole. Add the chicken pieces and brown them all over. Add the wine and season with salt and pepper. Cook for 5 minutes to evaporate the alcohol, then add the tomatoes. Stir in the rest of the stock and the mushrooms.