Pak Choi, very lightly stir-fried with a bit of garlic or ginger, is divine! Oyster sauce, soy sauce and sesame oil are all well suited, alone or together, to the delicate flavour of pak choi. If you want, add a bit of cornflour to the sauce to thicken. Try cutting 1 head crosswise into thin strips and frying it in a little oil for 2 minutes. Then add 2 tablespoons water, 1 tablespoon soy sauce, 1 tablespoon oyster sauce, and 1 tablespoon butter; cook for 2 minutes more and serve with fish or over steamed rice.