Stir-Fried Tangy Beef

This is a very simple, meat-and-vegetables stir-fry, the sort of dish one finds in a northern Chinese home or in a simple restaurant or stall by the roadside. Its charm is the mixture of tender beef, crisp vegetables, and a mildly spicy sauce with an undertone of sweetness.

• Chinese longbeans, sometimes called “yard-long beans,” are sold in bunches of about 2 pounds in Chinese markets and specialty produce stores, tied together at one end like a lively ponytail.