Place pork belly in a 5.5-quart dutch oven and add cold water to cover the pork by 1 inch (2 cm). Bring to a boil over medium-high heat. Turn to medium low heat and boil for 10 minutes. Skim the broth with a fine mesh strainer to get rid of the foam.
Add chili peppers, cloves, nutmeg, star anise, cinnamon, ginger, green onion, and Shaoxing wine. Bring to a boil over medium-high heat, then turn to lowest heat and simmer, covered, for 30 minutes.
Add light soy sauce, dark soy sauce, sugar, and salt into the pot and stir to mix well. Continue to simmer, covered, for an additional 1 hour. Skim off the oil from the top by using a fine mesh strainer.
Uncover, and continue to simmer for another hour or so, until the broth is reduced to about one fourth and has thickened slightly. Keep an eye on the pork during the last 30 minutes, because the broth can reduce very fast at the end and burn the bottom. You should have at least 1 cup of broth in the pot after reducing, in order to assemble the pork buns.