cut into 1-in pieces HEAT THE WOK over a high flame for 1 minute. Add the oil, and when the oil is very hot (this will take just a few seconds; pass your hand over it to feel the heat, or look for a wisp of smoke), add the salt, garlic and bok choy. A common mistake is to skimp on oil in stir-frying vegetables, which makes them dry out and burn. Use enough oil to coat the vegetables thinly but thoroughly. This may be prepared in advance and served cold.