Chop pork knuckle into small pieces with bones attached. Wash clean with water and remove hair. Simmer the meat in hot water with ginger and green onions for 30 minutes. Remove and set aside.

Heat up wok with sesame oil. Add in old ginger or Bentong Ginger and stir fry till fragrance. The ginger is best cut into thick slices or just smashed it in large chunks. Add in some salt. Pour the ginger into a clay pot or any pot for slow cook purpose.

Add 250ml black vinegar and 300ml water into the pot with the fried ginger and simmer it for 30 minutes.

Add in another round of 250ml black vinegar and 300ml water and simmer for another 30 minutes. You can add a few pieces dried chillies if you prefer more spiciness.

Add in the pork and simmer in slow cook mode for 1 hour until meat is soft. Add in sugar and slow cook for another 10 minutes till sugar dissolves. Adjust sugar to taste if you want more sweetness.

You can remove some oil on the top of the layer of the gravy. Some recipe add in black beans and hard boiled eggs and is optional. The gravy should taste sour and sweet with some spiciness of ginger.