Top-ranked recipe named "Tomato Oxtail Soup"
Remove extra fat from the oxtail chunks. You dont need to be very thorough with this preparation. Leaving some fat on the oxtail chunks is ok.
In a large pot, add water (enough to cover the oxtail chunks, based on your estimation, but dont put the oxtail chunks in the pot yet) and bring to a boil. Put the oxtail chunks in the boiling water for a minute or two, until the meat is no longer red. Empty the pot and rinse the oxtail chunks in cold water. Clean the pot. Put the oxtail chunks back to the pot. Add black pepper, the sliced onion and ginger roots. Fill to 2/3 of the pot with fresh water. Cover and bring to a boil on high heat.
Switch to medium-low heat to keep the soup stewing for about 3~4 hours. During this time, use a spoon to remove fat from the surface of the soup as often as needed. When the oxtail chunks are finally done (you can use a fork to test if the meat can come off the bones,) add tomato sauce to the soup, stir, and bring it to a boil on high heat. Use a spoon to remove the foams from the surface of the soup. Peel the potato and cut it into slices. Add the potato to the soup, bring to a boil and leave the soup stew on medium heat for another 30 minutes or until the potato is well cooked. Add salt to taste. Serve.