1. When you buy pork bones, ask the stall owner to cut them into large pieces and wash them when you come back.

2. Wash the watercress and carrots, and cut the carrots and sweet corn into large pieces.

3. Add water to the pot, add pork bones and bring to a boil, then skim off the foam.

4. Put all the ingredients into the pot, bring to a boil, and simmer for 2 hours.

5. After stewing, just add some salt to taste.

6. A very sweet soup.