Put the entire pork belly in a stockpot and add enough water to cover the meat completely. Bring the water to a boil, then turn down the heat to medium. Parboil the pork belly, uncovered, for 20 minutes, continuously skimming off the scum that forms on the surface. Drain, and let the pork belly cool. Then cut it into pieces about 1 1/2 inches square.
Combine the sugar with 3 tablespoons water in a wok over medium heat. Continue heating until the sugar syrup just begins to turn yellow. Add the cubed pork belly to the wok and brown it with the caramelized sugar, stirring the meat regularly to prevent burning. If you like, cover the wok with a splatter guard to prevent the fat from splattering.
Add the garlic, scallions, star anise (if using), both soy sauces, wine or Sherry, and stock (or water) to the wok. Bring the liquid to a boil, then transfer the contents to a clay pot or Dutch oven (or, if your wok has a lid, use it to cover the pan. Or, transfer the contents to a slow cooker.) Simmer, covered, over low heat, stirring the meat every 15 minutes to prevent scorching the pork on the bottom, for 1 hour or until the meat is tender when pierced with a knife—I cooked mine for about 1hr 45 minutes.
Remove the meat and put it in a bowl. Reduce the sauce over medium-high heat until it reaches the desired consistency. Return the meat to the pot and reheat before serving.