Have the butcher cut pork leg at about 2 inches apart but not all the way through. Under cold running water, rinse pork leg. Pat dry.
In a wide pan over high heat, heat 2 tablespoons of the oil. Add pork leg and sear on all sides. Remove from pan and set aside.
In a large pot, combine Chinese cooking wine, vinegar, soy sauce, sugar, star anise, and water. Over medium heat, bring to a boil, stirring regularly until sugar is dissolved.
Gently place pork leg into the liquid mixture and boil for about 5 minutes.
Lower heat, cover and continue to cook for about 2 to 2 1/2 hours or until meat is very tender and almost falling off the bone. Add more water in 1/2 cup increments as needed during cooking to maintain about 2 cups of sauce.
Rinse the mushrooms and mushrooms into 1-inch thick strips.
In a pan over high heat, heat the remaining 1 tablespoon oil. Add mushrooms and cook, stirring regularly, for about 1 minute or until heated through. Remove from pan and keep warm.
In the pan, add bok choy and cook, stirring regularly, for about 30 seconds or until tender yet crisp.
To serve, place pork leg on a serving platter. Arrange bok choy and shitake mushrooms around pork leg. Spoon sauce over the vegetables and meat. Serve hot.