Jiang Nan, like a batting machine, nonchalantly, repeatedly, rapidly, knocks out culinary triples and homers. The best-known item at this upscale chain is the Peking duck (also known as Beijing duck), a hard dish to master. Before roasting, it must be inflated to separate the skin from the meat. It must be lacquered and dried. Jiang Nan nails it: skin crisp, meat moist, handsomely presented with segments of shredded scallion, cuke batons, and hoisin. The Peking duck egg rolls are another hit: The oil-free skin, layered like filo, shattered to the tooth. The interior was not just ducky but Peking ducky, attached skin still conveying its flavor. There were