Rinse the beef thoroughly in several changes of lukewarm water. Place in a large heavy pot and add enough cold water to cover by an inch or two. Bring to a boil and skim off the foam as it forms. Add the ginger, star anise, if using, and salt, reduce the heat, and simmer, partly covered, for the next 5 hours
Pour the broth through a sieve or strainer into a bowl. (Set the bones and meat aside if you wish, to be served with rice or noodles, or discard them). If not using the broth immediately, let it cool completely, then store in a well-sealed container in the refrigerator, or freeze in 2-cup containers
Notes
NOTE: Save the tender oxtails you've cooked for so long. I served them with the Tsampa soup :)