1. Ingredients: 1000 grams of pork leg bones, 1 corn, 200 grams of yam, appropriate amount of cooking oil, appropriate amount of cooking wine, appropriate amount of salt, and appropriate amount of green onions.

2. To choose fresh pork leg bones, first look at the bright red and shiny color of the bones.

3. Soak the bones in clean water for 5 minutes to soak out the blood.

4. After cleaning the bones, add cold water to the pot. After boiling, blanch the bones for about 5 minutes to remove the foam.

5. While the pork leg bones are blanching, clean the fresh corn and cut it into small pieces for later use.

6. Peel the yam, cut into small pieces, rinse with clean water, drain and set aside.

7. After blanching the pork bones, rinse them with cold water, drain them and set aside.

8. Put the ingredients into a casserole, add an appropriate amount of boiling water, bring to a boil over high heat, then turn to medium to low heat and simmer slowly for about 2 hours.

9. After two hours, open the lid, add an appropriate amount of salt, stir evenly, and simmer for another 5 minutes before eating.