Trim 5 cm (2 inches) from the ends of the choi sum, then cut it into 5 cm (2 inch) lengths. Wash thoroughly.
Heat the oil in a wok over a high heat until the oil starts to shimmer. Add the garlic and salt and stir-fry for 15 seconds, then tip in the choi sum and stir-fry for 1 minute.
Add the rice wine and water and stir-fry for 2–3 minutes, until the choi sum is tender and most of the liquid has evaporated. Stir in the sesame oil and serve immediately.