Think of mild-flavored, juicy bok choy as an invitation to experiment in the kitchen. It's especially good with earthy mushrooms. Thoroughly drying the bok choy before cooking ensures that you don't end up with a watery sauce. As the tofu cooks with bok choy, it will break down into a sauce.
1. Trim bases of bok choy and separate outer leaves from stalks, leaving the smallest inner leaves attached. Rinse and thoroughly dry bok choy in a salad spinner.
2. Heat a wok or large frying pan (not nonstick) over medium-high heat until hot when you wave your hand over the bottom. Add vegetable oil, garlic, and ginger and stir once; then immediately add mushrooms and stir-fry until they just begin to brown, 1 to 2 minutes. Toss tofu with 1/4 tsp. pepper and stir-fry tofu until it softens and starts to look custardy, 2 to 3 minutes.
3. Add rice wine and cook 30 seconds. Add bok choy leaves and stalks and cook, tossing with tongs, until beginning to wilt, about 1 minute. The wok may seem crowded, but the leaves wilt quite a bit.
4. Add soy sauce, sesame oil, salt, and remaining pepper; cook, tossing often, until bok choy is tender-crisp, another 1 to 1 1/2 minutes.