Trim excess fat from pork belly and divide into 2 pieces.

Cut pork belly to an even thickness.

Pierce the pork belly many times with a fork.

Place pork belly in a plastic Ziploc bag.

Rub sugar into all sides of the pork and let sit for 30 minutes.

Mix grated onion, soy sauce, oyster sauce, Shaoxing wine, sesame oil, and grated garlic in a container.

Add the marinade to the bag with the pork, remove excess air, and seal the bag.

Ensure the pork is fully immersed in the marinade and refrigerate overnight.

Preheat the oven to 480F/250C.

Transfer the marinated pork and marinade to a small pan.

Remove the pork from the marinade, reserving the marinade, and place the pork in a roasting pan.

Roast the pork at 480F/250C for 7 minutes on one side, then turn and roast for another 7 minutes, or until cooked through.

Check for doneness by piercing with a skewer; juices should run clear.

Add 4 tablespoons of water to the reserved marinade in the small pan and bring to a boil.

Simmer the marinade over low heat and thicken with a slurry of katakuriko potato starch and water.

Be careful not to thicken the sauce too much.

Slice the roasted pork belly into 1 cm thick slices.

Spoon the thickened sauce over the sliced pork belly and serve immediately.

If freezing marinated pork, defrost in the refrigerator the day before cooking or in a bowl of cold water.

Consider roasting the pork wrapped in foil for a juicier result.

Adjust roasting time based on the thickness of the pork.

Lamb chops can be substituted for pork belly.