To prepare the pork, trim and cut the pork belly into 1-inch pieces.
To sear, in a pan over high heat, add the cooking oil and the pork belly. Stir-fry until lightly browned.
To build flavor, add the garlic and stir-fry until fragrant. Add the bay leaves, the black peppercorns, the soy sauce, and the sugar if using. Cook for 1 minute.
To braise, pour in the water and bring to a simmer. Cover, reduce to low heat, and cook for 45 minutes until the pork is tender.
To finish, uncover and pour in the vinegar. Simmer uncovered for 15 minutes without stirring to allow the vinegar to mellow and the sauce to reduce.
Serve hot with steamed rice.