Heat 2 tablespoons of oil in a large heavy saucepan. Add the pork belly and fry until nicely browned.
Add the smashed garlic cloves and coriander roots then fry until fragrant.
Add the radish, cabbage, greens and dark soy sauce. Add enough water to three-quarters of the ingredients’ level. The mustard greens will shrink considerably. Bring to a boil and simmer for an hour or two or until the pork is very tender. Add water as needed to keep the ingredients covered.
When the meat is tender heat a small frypan over medium heat. Add the oil and garlic. Fry until fragrant and golden brown.
Add the black bean paste and sugar. Fry until fragrant.
Add this mixture to the saucepan. Stir well. Adjust seasoning with more sugar or fish sauce to taste.