The night before you intend to serve this dish, peel and cut the onions into sixths and sprinkle with sea salt. After about two hours wash and dry onions, place in a bowl and pour over the balsamic vinegar. Cover and refrigerate overnight.

Remove pork from the fridge about 3 hours before cooking. Using a sharp blade, make cuts in the skin from top to bottom, in the same direction, about 3mm apart. Then cut the other way to create small diamonds: don't cut into the flesh. Rub red wine vinegar into the skin, then rub salt into the skin. Set the pork aside for about an hour to dry.

Preheat oven to 180C. Put the pork on a wire rack in a roasting tin and cook in the oven for 30 minutes. Check the meat's core temperature - it should be about 71C. Remove pork from the oven and turn temperature down to about 160C. Rest pork in the oven for about 30 minutes. Be sure to check the pork's core temperature rises to about 75C.

Just before serving, heat the vegetable oil in a saucepan until just smoking. Remove pork from the oven, and with a spoon, pour over the oil over the skin to complete the crackling.

Cut pork into thin slices. Drain and add the onions. Drizzle the balsamic vinegar and olive oil over the meat, season with salt and pepper to taste, and serve.

Tip: Mustard fruits are a great accompaniment to serve with the pork belly dish.