Marinating meat before cooking is an essential step in most stir-fries. In this dish, a mix of egg white and cornstarch coats the chicken and a quick blanching in a little oil in the wok preserves its succulence—a technique called velveting. Like the recipe for red-cooked pork belly (see Red-Cooked Pork Belly), this one comes from Deng Haiyan, one of the most adept cooks I've met here in Beijing. Once she's blanched the chicken, she sets it aside. Then, julienned ginger and leeks go into the wok and release their perfume into the hot oil; celery, added next, cooks until crisp-tender and faintly sweet. The payoff comes when the chicken is reintroduced to the wok: the cornstarch-egg white coating soaks up the flavors of the aromatics, and the bright, crunchy celery contrasts beautifully with the silky texture and delicate flavor of the chicken.