Cut the neck of the pork into slices (do not cut all the way through) to create pockets for stuffing. Salt the roast and season with pepper. Then pour some thinly sliced pork belly into the first pocket. Fill the next pocket with plenty of onion rings. Always fill the pockets alternately. Place the filled roast in a roasting pan with a lid and cover. First let it steep in the refrigerator for about 12-24 hours.
Cook in a preheated oven at 225 ° C for about 2 to 2.5 hours.