Perfectly rolled roast pork (Porchetta)

Ingredients

• - 2 kg boneless pork belly, skin scored by the butcher
• - 1 tablespoon vinegar (white wine or apple cider)
• - 1 teaspoon baking powder
• - 1.5 tbsp fennel seeds
• - 1 tbsp black peppercorns
• - 1.5 teaspoon chili flakes
• - Zest of 1 lemon
• - 6 cloves of garlic, pressed
• - 1.5 teaspoon rosemary, sage or thyme leaves
• - 1 kg of potatoes
• - Oil, salt and pepper if necessary
• - Half a red onion, finely chopped
• - 2 spring onions, finely chopped
• - 2 tablespoons capers
• - Handful of parsley