Baby bok choy is more tender than the vegetable is at full size -- try it with using this simple preparation.
Heat oil in a large skillet over medium-high heat until hot but not smoking. Add bok choy, and cook, turning once, until just beginning to turn golden, about 2 minutes. Add stock and soy sauce. Cover; reduce heat to medium, and simmer until bok choy is tender, about 5 minutes. Transfer bok choy to a serving platter, reserving cooking liquid in skillet.
Cook liquid over medium-high heat until it is reduced by half, 1 to 2 minutes. Pour over bok choy, and serve.