Place the oxtails in a pot of cold water. Bring it to a boil for ten minutes. This removes grey foam and dirt from the meat. Drain the water and rinse the bones very well.

Fill the pot with fresh clean water again. Add the ginger, star anise, and orange peel now. Drop in the raw peanuts and the dried mushrooms. Bring the liquid to a soft boil on high.

Turn the heat down to a very low setting. Cover the pot with a lid for three hours. The meat should be very tender by this time. Check the water level every hour to stay full.

Add your soy sauce and salt to the pot. Taste the broth to see if it needs more. Remove any excess oil floating on the very top. The liquid should look clear and dark brown now.

Chop the mustard greens into large chunky pieces. Toss them into the boiling soup for two minutes. They should stay bright green but feel quite soft. Turn off the heat immediately so they do not brown.

Grate fresh ginger into small bowls for your guests. Pour soy sauce over the ginger for a dip. This is the traditional way to eat the meat. Serve the soup hot with a side of rice.