Combine all of the ingredients except the pork and skewers in a saucepan. Heat on med/low for about five to ten minutes, stirring everything together until it thickens. Set it aside and allow it to cool.
The cut of pork you wish to use is up to you; if you get pork belly, try and get the meatiest cut you can. You definitely want to get something that’s fairly well marbled, and something that’s super lean like pork loin will just taste like pork jerky. Regardless of the cut, be sure to cut off the skin and cut the pork into chunks about 1″ in size.
Once the sauce is cool, put half of it in a gallon-sized ziploc bag with the pork pieces. Put the other half of the sauce in a container and then put both the pork and the sauce in the fridge overnight.
The next day, soak the bamboo skewers in cold water for 30 minutes, then skewer the pork chunks.
Preheat the grill for about 10 minutes on med/high heat. Turn off the heat on one side of the grill, and place the skewers on the unheated side. Grill using indirect heat for an hour, turning the skewers after 30 minutes. Your optimal grill temp should be around 250-300 degrees. During the last 30 minutes, take out your reserved char siu sauce and allow it to warm to room temperature.
Lastly, char the pork skewers on direct (medium) heat for a few minutes, brushing on the char siu sauce as it cooks. That’s it! Take the pork off the skewers and serve immediately.