Preheat the oven to 300°F.
Fill a large pot with water and bring to a boil over high heat.
Add the beef and 2 tablespoons sliced ginger and return to a boil. Drain the beef and set aside.
In a cheesecloth, tie together the cinnamon stick, star anise, and 1 inch of ginger.
In a braising dish with a lid, combine the soy sauce, rice wine and beef. Add enough water so that the liquid comes halfway up the sides of the meat. Tightly secure the lid and braise in the oven until the meat is falling-apart tender, about 90 minutes.
Taste and adjust the seasoning. Remove the meat from the sauce.
Meanwhile, combine the mustard greens, vinegar and salt in a bowl. Let sit until the greens are wilted and pickled.
Bring a large pot of salted water to a boil. Add the noodles and cook according to the package directions. Drain the noodles, return to the pot and toss with oil to prevent sticking.
To assemble the soup, place noodles, beef, and bok choy in deep soup bowls. Ladle in the broth and top with sliced green onions. Serve with pickled mustard greens on the side.