Heat a wok until just smoking. Add the vegetable oil and, when hot, stir-fry the ginger until fragrant. Add the bok choy and cook for 1–2 minutes, or until the leaves are just limp, then deglaze the wok with the shaoxing and add the stock, sugar and salt. Stir-fry for another minute, or until the bok choy is just cooked. Transfer to a serving plate, spoon over the juices and drizzle with sesame oil to serve.