Rinse pork belly and pat dry with paper towels. Slide it into a sous vide bag. If your sous vide bag is not big enough to hold an entire piece of pork belly, cut the meat to divide into two or three portions if needed.
Combine all marinade ingredients except the star anise in a food processor. Blend until smooth. Pour the marinade into the sous vide bag over the pork. Gently tilt the bag to allow the marinade to cover the entire piece. (If using multiple sous vide bags, divide the marinade into equal portions for each bag.) Drop in the star anise and seal the bag(s) using a vacuum sealer or a hand pump. You can leave the pre-packed pork belly in your fridge to marinate overnight, or you may cook immediately.
When ready to cook, preheat water to 176°F using a sous vide immersion circulator. (I use Anova.) Lower the pork belly bag(s) into the water and make sure the pork is immersed. Cook for 7 hours.
Once the pork is done, remove the bag(s) from the water. Open it, transfer the pork belly onto a cutting board, then carefully pour the cooking liquid into a small saucepan. Discard the star anise.
Bring the cooking liquid to a boil and simmer down to half. If the consistency is not to your liking, dissolve 1-2 tablespoons cornstarch in cold water and add to the sauce, stirring often until the sauce is thickened.
Cut the pork belly into slices, 1-inch bites, or 2-inch pieces; plate it and pour a generous amount of sauce over. Pass the extra sauce around the table. Enjoy!