Using a sharp knife, cut 1 inch slits halfway into the meat side of the pork belly. This helps the marinade penetrate deeper.
Parboil the pork belly by adding 1 inch of water to a pot and bringing it to a boil. Add in the pork belly, meat side down, making sure the pork belly skin sits above the water and remains dry. Parboil for 5 minutes to draw out impurities. After 5 minutes, remove the pork belly and pat it dry.
Mix together five spice powder, ½ teaspoon salt, white pepper, and Shaoxing wine until it forms a paste. It'll be thick and fragrant. Set aside.
Using a toothpick, fork, or meat tenderizer, prick small punctures into the pork skin, being careful not to puncture deeper than the skin.
Rub the five spice paste all over the meat side only, working it into the slits.
Wrap the pork belly in foil so the meat is fully covered but the skin is facing up and fully exposed. Brush the skin with vinegar and allow it to dry for a few seconds.
Add the salt over the pork belly skin so it's even and well coated. Press down lightly to pack it.
Air fry at 200F for 10-15 minutes or until the salt crust is completely dry and can be picked up.
Remove the salt crust and brush off any remaining excess salt with a paper towel. Lightly brush the skin with neutral oil and air fry at 400F for 10-15 minutes until the skin is puffed up and crispy. If there are parts of the skin that is browning faster than others, cover it with foil to keep it from burning.
Let it rest for 10 minutes before cutting into slices. Enjoy with banh hoi, fresh herbs and veggies, and nuoc mam cham!