In a medium stock pot, bring water to a gentle boil. Add salt, garlic, peppercorns, and bay leaf.
Once the water with aromatics begin to rigorously boil, gently add the pork belly slab, skin side up.
Skim the scum. Turn pork belly slab after every 10 minutes.
Carefully remove pork after 45 minutes to 1 hour or when pork belly slab is fork-tender. Add more water halfway through, if needed.
Cool for 30 minutes or more. Place in an airtight container lined with paper towels. Refrigerate overnight.
Next day, gently transfer pork belly slab onto the Air Fryer tray, skin side up. Let it sit at room temperature for 15 to 30 minutes.
Lightly brush pork skin with apple cider vinegar.
Slowly insert the Air Fryer tray into the pre-heated Air Fryer at 400F (205C) in the middle cooking chamber, near the rotisserie catch. Air Fry pork belly slab for 30 minutes.
Brush pork skin with the remaining apple cider vinegar at the last 10 minutes.
Remove pork belly slab once crisp and golden.
Let it sit for 5 to 10 minutes before chopping into bite-sized pieces.
Serve with your favorite dipping sauce.