Fesenjan duck in pomegranate and walnut sauce

Fesenjan - a Persian stew - is often served on special occasions. Although traditionally made with duck, as here, or game, such as squab pigeon or pheasant, it is equally good made with chicken. The sauce should be thick and its flavour full of sweet-and-sour overtones. If pomegranate molasses are not available, use the same amount of pomegranate juice instead.