Heat the wok over a high heat until smoke rises. Add the oil and swirl it around. Add the ginger, then the white scallions, and let sizzle for a few seconds to release their aroma. Add the cabbage stems and, sliding the wok scoop to the bottom of the wok, flip and turn for about 2 minutes. Then add the leaves and stir-fry for another 2 minutes. Reduce the heat, cover the wok