Inspect the pork belly’s skin for bristles. A few stray hairs is fine, but if there are a lot of bristles, heat up a wok til it’s smoking and press the skin against the wok to singe off the hairs. Blanch the pork by placing the whole slab in a pot, covering with cold water, and bringing to a boil on high heat. Boil for one minute, then remove from heat and drain, rinsing off any scum clinging to the pork with cold water. Set aside.
While the pork is cooling, prep your aromatics. Slice off five good pieces of fresh ginger and chop 3 whole scallions into rough segments (chopping them in half and then half again should do it). Choose a pot (preferably heavy earthenware, with a lid and vent hole) that will hold the belly cubes snuggly in one layer. Scatter the scallions evenly across the bottom of your pot, then lay the slices of ginger on top. Try to make sure the bottom of the pot is completely covered.
*If your pork is thicker in some parts, or generally a lot thicker than 1½ inch: Use your fingers and a paring knife to remove a “layer” of lean muscle from the bottom. Since the meat is blanched, it should be easy to find the seam between muscles. Use the knife to help peel back the silverskin, but try to avoid piercing or cutting the muscles. Once you have a neat, trimmed slab, slice it into even squares. Set aside the extra lean meat for some other use.
Lay the squares of blanched pork belly skin-side down on top of the bed of scallions and ginger. If using spices, measure out ½ teaspoon red Sichuan peppercorns and ¼ teaspoon fennel seed. Tie them up in a cheesecloth and tuck the bundle into the pot as well. Add 1 cassia stick.Add 1 cup Shaoxing wine, ¼ cup light soy sauce, ⅓ cup rock sugar and 2 tablespoons of oyster sauce to the pot. The pork belly cubes should be half submerged in liquid.Cover the pot and bring to a boil over medium-high heat. As soon as it reaches a boil, turn it to the lowest possible setting to simmer lazily.
Simmer for 2 hours, then check the pork—it’s done when the fat looks more translucent than white, and a chopstick slides into the skin with no resistance. If the meat isn’t ready yet, cover and continue simmering and checking for 30 more minutes at a time.
When the pork has reached the right texture, flip the cubes skin-side up and turn heat to medium-high. (If you leave them skin-side down, the skin will stick to the bottom of the pot as the braising liquid reduces). Cover and let the liquid reduce via the steam hole for 20 minutes, which helps keep the skin from drying out. The liquid has adequately reduced into a rich sauce when it starts looking very foamy. Be careful to not let the sauce get too thick or burn while reducing—there will be a thick layer of oil over the sauce that may deceive you. You can test the sauce by spooning it over the pork—it should coat the pork, giving it a deep chestnut gloss. If serving immediately, gently scoop up and plate the pork belly cubes skin-side up. Pour off some of the excess grease from the sauce and strain the remainder, then spoon the sauce on top of the pork belly.If serving the next day, refrigerate overnight and remove the congealed fat from the top. To reheat, plate pork belly and sauce (right over raw baby bok choy if you’d like) and steam for 10 minutes.