Combine the soy sauce, sugar, mirin, oyster sauce, mushroom soy, green onions, star anise, cloves, peppercorn blend, cinnamon sticks and ginger slices in an 18-quart container. With a large whisk, mix the ingredients together. Make sure all the sugar at the bottom is properly stirred into the liquid. Gradually pour the water into the container and continue to stir.
Cut the pork butt in 2-inch square pieces. Trim all the hard fat off and leave about a quarter of the soft fat on the meat. Set the pork in a deep cooking pan, and, using a ladle, pour the soy marinade mix over the meat, make sure all the meat is covered in the liquid. (Any extra soy-ginger marinade can be put away and used again on a later date.) Add the dried black mushroom and bay leaves to the liquid, spreading them evenly throughout the pan. Tightly wrap the pan with heavy-duty foil and refrigerate overnight.
The next day, preheat the oven to 350 degrees F. Make sure the foil is tightly sealed around the pan and cook until the pork is fork tender, about 3 hours. Take the pan out of the oven and remove the foil. With a fork and tongs pull at the pork. It should easily tear off to assure it's fully cooked.
When cutting the pork butt, the size can vary. It does not have to be exactly 2 inches. But make sure the cuts are all about the same size so the pork meat can evenly cook in the oven.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.