Place the 3 lb pork belly skin-on, slab cut slab in a large Mixing Bowl and cover with 8 cups water enough to fully submerge the pork. Add the smashed 4 cloves garlic smashed, 3 piece bay leaves, whole 1 tbsp whole black peppercorns, 1 tbsp salt, and 1 tsp fish sauce added to the boiling water for depth (if using). Bring to a boil over high heat, then reduce to a steady simmer. Cook uncovered for 60–75 minutes, or until the 3 lb pork belly skin-on, slab cut is completely tender when pierced with a fork and the skin is soft.

Remove the 3 lb pork belly skin-on, slab cut from the pot and transfer it to a Wire Rack set over a Baking Sheet. Pat the skin and all sides thoroughly dry with paper towels — this is the most important step for achieving a crackling-crispy skin. Allow the 3 lb pork belly skin-on, slab cut to air-dry at room temperature for at least 20 minutes, or refrigerate uncovered for 1–4 hours for even better results.

Pour 4 cups vegetable oil for deep frying into a deep Skillet or heavy pot to a depth of at least 2–3 inches. Heat the oil to 350–375°F over medium-high heat. Carefully lower the dried 3 lb pork belly skin-on, slab cut into the hot oil, skin-side down first. Fry for 8–12 minutes, turning occasionally with Tongs, until the skin is deeply golden, blistered, and crackling all over. The internal temperature should reach at least 165°F. Work in batches if needed to avoid crowding.

Transfer the fried 3 lb pork belly skin-on, slab cut to a Wire Rack or paper-towel-lined plate to drain excess oil. Let it rest for 5 minutes before slicing into bite-sized pieces with a sharp Knife. Serve immediately with steamed white rice, ½ cup spiced cane vinegar or dipping vinegar with chili and garlic, and 1 can Mang Tomas liver sauce store-bought, for dipping for dipping.