Prepare the pork belly: Pat 250g pork belly completely dry with paper towel. Using a knife, sharp skewer or metal toothpick, poke as many holes as possible into the skin. Flip over and score the meat side only (not through the fat or skin) with shallow cuts 1–2cm apart.
Season the meat (not the skin): In a bowl, mix 1/2 tsp salt, 1/2 tsp white sugar, 1/2 tsp five-spice powder, 3 tsp Shaoxing wine or dry sherry (or 2 tsp white wine + 1 tsp water), and 1/2 tsp white pepper. Rub evenly over the meat side only, pushing seasoning into the cuts.
Wrap and salt the skin: Wrap the meat portion tightly with foil, leaving the skin exposed. Brush 1 tbsp white vinegar over the skin and sprinkle 1 tbsp salt evenly on top. Place uncovered in the fridge overnight.
Dry the skin: Remove pork belly from fridge. Brush another 1 tbsp white vinegar over the skin. Air fry skin side up at 90°C for 40 minutes until the skin looks slightly translucent and dry. If the skin still looks damp after 40 minutes, add another 5–10 minutes at 90°C.
Oil the skin: Brush 1 tbsp neutral oil evenly over the skin.
Final crisping: Air fry skin side up at 200°C for 25 minutes until the skin bubbles and puffs. Check every 5–8 minutes to prevent burning. If parts brown too quickly, loosely place a small piece of foil over that area.
Rest and slice: Rest pork belly for 10 minutes before slicing with a heavy, sharp knife. You should hear that crisp crunch.