Place pork belly skin side down in a large pot and add enough water to completely submerge the meat.
Add garlic, bay leaves, peppercorns, and soy sauce. Bring to a boil over medium-high heat, then lower heat and reduce to a simmer.
Cover and cook until pork skin can be pierced with a knife with no resistance (about 1 hour).
Transfer pork to a wire rack set on a rimmed baking sheet and season liberally with salt all over. Refrigerate pork until the skin has completely dried (6 hours or overnight).
Remove pork from refrigerator and cut into 3/4-inch slices.
Fill a wok or Dutch oven with at least 4 inches of oil and heat to 375°F over high heat. Working in batches, fry pork until deeply browned and skin has bubbled and crisped (7 to 10 minutes).
Transfer pork to a paper towel-lined plate and season with salt to taste. Cut pork slices into 1/2-inch pieces.
Serve immediately with vinegar for dipping.