Heat the oil in the wok.
Brown and discard the garlic.
Stirfry the green beans for 3 minutes.
Add the chicken broth, salt, and sugar.
Cover and steam over moderate heat for 3 to 4 minutes, until beans are tender but still bright green and crisp.
Stir the cornstarch mixture and add it to the wok.
Cook, stirring, until the sauce is thickened.
Serve at once.
Variations.
Green Beans with Black Bean Sauce: Combine 1 tablespoon black bean sauce, 1 teaspoon dry sherry, and 1 teaspoon sugar and stir into the beans just before serving.
Green Beans with Water Chestnuts: Add 8 to 10 water chestnuts, sliced, to the beans just before the stock is added.
Green Beans with Sweet and Sour Sauce: Add 2 teaspoons lemon juice and 1 teaspoon sugar to the beans just before serving.