High-heating roasting caramelizes bok choy, lending it an alluring sweet edge. It starts out with a gentle mustard-like flavor, but roasting tames much of that sharpness. The process creates texture contrast, transforming the tender leaves to a potato-chip crunchiness, the broad base to a moist succulence. It’s the best way to cook it. While the bok choy is in the oven, make a quick 5-ingredient ginger sauce to pour over the vegetables.