Quarter the pork butt lengthwise. Rub them with two tablespoons of sugar and place them in a large bowl and set aside for 15 minutes. Pour off any excess liquid.
In a small bowl, combine the remaining two tablespoons of sugar, thin soy sauce, hoisin sauce, black soy sauce, rice wine, ground bean sauce, sesame oil, and pepper. Stir to combine.
Pour mixture over the pork, making sure the pork is well coated.
Loosely cover with plastic wrap and refrigerate overnight, turning the pork from time to time.
Preheat the oven to 420 F. When ready to roast, let the pork come to room temperature, allowing it to sit for at least 20 minutes.
Remove the pork from the marinade and place on a baking pan, which you will put on the middle rack of the oven and bake for 20 minutes or until the pork registers 155 degrees.
Remove the pork belly and transfer it to a plate and allow it to cool (at least 10 mins) to just about room temperature. When ready, cut the pork belly into small dice.