Put the pork belly, in one or two pieces, into a dutch oven or soup pot, preferably nonstick (which makes it easier to caramelize the meat without burning in the next step). Add cold water to cover. Bring to a boil, then turn the heat down to medium and cook, uncovered, on a low boil for 20 minutes, skimming off the scum that forms on the surface. Remove the pork belly and allow it to cool enough to cut into pieces about 1½-inch wide, each piece retaining fat and meat.
Wash the pan, and add 3 tablespoons sugar and 4 tablespoons water. Cook over a medium fire until the caramel starts to turn a light brown. This will take a few minutes, but watch the sugar carefully because when it starts to turn color it does so quickly. Add the pork pieces and let sear and caramelize on one side until they are a nice dark color. Turn the pieces over and caramelize the other side. The sugar should be a deep brown but not burning.
Add 1½ cups water with the garlic, scallion, star anise, dark soy sauce, light soy sauce and Shaoxing wine. Bring to a boil, then lower heat and cook, covered, at a just-bubbling simmer for about 1 hour and 15 minutes, stirring every 15 minutes or so, until the meat is tender.
Remove the pork pieces to a bowl, and cook the sauce over a medium-high heat until it reduces to your desired consistency (anywhere from a thick sauce to a thick glaze), about 5 minutes for a thick sauce. When you are ready to serve, add back the pork pieces and reheat. Then remove the pork to a serving bowl. Let the sauce sit for a minute to separate, then carefully pour off the accumulated fat, which will pour out first as you tip the pan. (Or use a fat separator.) Pour the remaining sauce over the pork and serve with rice or with fold-over bao as sandwiches.