• Add the beef shank into a large pot and add enough cold water to cover. Cook over high heat, stirring occasionally to prevent the bottom from sticking. After the water is boiling, cook for 5 minutes. Drain the beef and discard the broth. Rinse any brown foam from the beef with tap water if needed.
• In a dutch oven (or the same big pot you just used), add 2 tablespoons of oil and heat over medium heat until the oil is shimmering. Add the scallion, onion, carrot, garlic and ginger. Stir and cook for 4 to 5 minutes.
• Add the doubanjiang. Stir to coat everything well, 1 to 2 minutes.
• Pour in the Shaoxing wine. Scrape any browned bits off the bottom of the pot.
• Add back the blanched beef and pour in 8 cups of water. Add the tomato, daikon, soy sauce, fennel seeds, star anise, Sichuan peppercorns, and cinnamon sticks. Cook over medium-high heat until it comes to a boil. Lower the heat to medium-low. Cover and simmer for 2 hours, until the beef turns tender. Taste the broth and adjust seasoning by adding salt, if needed.
• Once the soup is done, transfer the beef pieces to a big plate to cool. Use a spider to remove and discard the solid ingredients from the soup. You can use a colander to strain the soup further for a clear broth. (*Footnote 5) At this point, you can store the broth and the beef for future use.

For the Mustard Green Pickle

• While the broth is simmering, prepare the pickled greens. Add the oil into a medium pan and heat over medium-high heat until shimmering. Add the garlic and chilis. Stir and cook for 30 seconds to release fragrance.
• Add the pickled mustard greens. Stir and cook until any excess liquid has evaporated, about 2 minutes. Add the sugar. Cook and stir until the sugar has dissolved, 2 minutes or so. Transfer everything to a small bowl and set aside.

Assemble the Noodle Bowls

• Warm 1 to 1 1/2 cup of soup for each bowl (the amount of soup depends on the size of the noodle bowl). After boiling, cover and turn to low heat to keep warm.
• When it’s possible to handle the beef with your hands, slice the beef into 1/2” (1 cm) thick pieces against the grain. Add the sliced beef to the hot soup to bring it up to serving temperature.
• Heat a pot of water over high heat to bring to a boil. Add 3 to 4 pieces of bok choy per bowl to the water and blanch for a minute, or to desired doneness. Transfer to a plate using a slotted spoon. Quickly rinse with cold tap water to stop cooking, drain, and set aside.
• Cook the noodles according to package instructions in the same pot. Drain and rinse with cold tap water briefly to stop cooking. Drain again.
• To each serving bowl, add the noodles, pour in the soup, top with the sliced beef, mustard greens, and bok choy. Sprinkle with scallion slices to garnish. Serve immediately as a main dish.