Boil chestnuts, remove skins and chop or mince nuts finely for stuffing. Cook Spanish onion in water until tender, chop finely, add to chestnuts, season well and bind with egg. Stuff duck with chestnut mixture, truss, lard with bacon, if liked. Slice vegetables for mirepoix (foundation), place in a large saucepan with butter, lay duck on vegetables, cover pan, fry gently for 20 min.; then add bouquet garni, spices, and enough stock to come three-quarters of the depth of mirepoix. Cover with a buttered paper, put on lid, simmer gently until duck is tender—about 2 hr. Add more stock if necessary to prevent burning. Heat Espagnole sauce, add wine (if used) and jelly, reheat and season to taste. Remove paper and trussing string from duck, and place it in a hot oven (425°–450° F., Gas 7–8) to crisp the bacon. Serve on a hot dish, with a watercress garnish, if liked: serve sauce separately.