Soak oxtail in water for at least two hours, until all the blood seeps out of the bone. Drain.

Place oxtail, ginger, shaoxing wine, and water in a pot and bring to a boil. Cook for 2-3 minutes, then drain.

Add oxtail and ginger back in a new pot of cold water, making sure to cover bones completely. Add leek rounds. Bring to a boil, then reduce heat to medium. Cover and continue boiling for 3-4 hours, adding more water if necessary. A moderate boil (not a simmer) should be continuous throughout the cooking period.

At the 3 hour mark, add in daikon slices and continue boiling for another 45 minutes. Check to see if the daikon is soft but not mushy. Remove daikon and set aside.

If the beef has started to fall off the bones, set that aside and reserve. Continue simmering the bones if you want them even more tender.

Remove broth and set aside in a large bowl. Cover bones in pot with water and bring to a rolling boil and keep at that moderate boil for another 3 hours. Remove from heat and pour broth into that same bowl of reserved broth.

Cover with plastic wrap and place in fridge overnight. This allows the fat to solidify and float to the top.

Remove fat in the morning. Pour back into a pan and reheat (including remaining bones). Meanwhile, make rice. Mix beef with garlic, scallions, soy sauce, and gochugaru, if using.

Divide rice into bowls. Ladle oxtail broth over rice. Serve with beef, radish, fresh scallions, and kimchi.