In a large pot or bowl, submerge the oxtail in cold water and soak for an hour. This will draw out the blood from the meat. Drain and replace the water every 20 minutes.

Drain the oxtail. Trim the excess fat, but it is not necessary to trim the silver skin (the thin membrane that encases the meat).

In a large pot, add the oxtails and cover with water. Bring to a boil over high heat. Foam and scum will come to the surface. Once it has come to a boil, drain and give the oxtails a quick rinse. Clean the pot of residue. Note: This step is important. I've tried omitting this step, but the broth ended up tasting metallic and not so great.

Place the oxtail and about 14 cups of water into the cleaned large pot or Dutch oven that is at least 7 quarts. Place the pot over high heat and bring the oxtail to a boil. Skim any impurities and scum that rise to the surface.

Lower the heat to medium low, partially cover the pot, and simmer until the beef starts to separate from the bones, about 3 to 4 hours. The soup will reduce as it cooks so add about 2 cups towards the end.

With a slotted spoon, remove the oxtail and set aside in a clean bowl. With a strainer, skim the soup of any impurities and discard. And with a large spoon, skim as much fat as you can.Note: If you have the time, you can cool the soup to room temperature and then stick the pot into the refrigerator to completely cool the soup, typically overnight. Once the soup is cooled, the fat will coagulate at the surface and will be easier to discard. If you are doing this, don’t forget to refrigerate the oxtail!

Add the black peppercorns, 1 tablespoon of kosher salt, and garlic cloves. Bring the soup to a boil over high heat, lower the heat to medium low and simmer for about 20 minutes. You can add another 1 cup of water if the soup has greatly reduced.

To serve, divide the oxtail evenly among large soup bowls. Discard the peppercorns and garlic from the pot. Ladle the broth over the oxtail. Sprinkle a handful of green onions in each bowl. Serve hot and each person can add salt to their liking.