1. Stir the sugar with soy sauce, rice wine vinegar and chili-garlic sauce (if using) in a small bowl until the sugar dissolves. Stir in the cornstarch. Reserve. 

2. Place the bok choy in a frying pan that’s wide enough to fit the bulbs all in a single layer. Add the water, cover and bring to a boil. Cook 3 minutes or until the stems are tender-crisp when poked with a sharp knife. Take off the lid and cook, shaking the pan a few times, until the pan is dry, about 1 minute. 

3. Stir the soy sauce mixture and add it to the pan. Cook, stirring constantly, 10 to 30 seconds or until the sauce thickens and coats the bok choy. Serve immediately.