I don’t bother doing twice cooked pork belly often, mainly because its pretty good cooked just once. The benefit of cooking it twice is that you press it underweight over night once cooked and that forces a lot of the fat and gelatinous material out, leaving a cleaner meatier pork belly. I did this one and then had a Char Siu sauce and a garden salad with it. When twice cooking, leave belly in vac sealed bag it comes in from the super market or vac seal yourself. Then cook sous vide style at about 58 -60deg for an hour or so. Cool and press overnight and then cook to caramelise.