Rinse and prep: Rinse the pork belly under cold water and pat dry. Trim any loose bits.
Keep the slab whole for even cooking.
Build the broth: In a large pot, add water, onion, garlic, ginger, scallions, soy sauce, rice wine, sugar, peppercorns, bay leaves, and radish/daikon if using.
Add the pork: Gently place the pork belly into the pot. Liquid should cover it by at least 1 inch. If not, add a little more water.
Bring to a boil, then simmer: Bring to a strong boil over high heat for 5 minutes.
Skim off any foam. Reduce to a gentle simmer, cover partially, and cook for 60–75 minutes, turning the pork once halfway through.
Check doneness: The pork is ready when a chopstick or fork slides in easily and the center is no longer pink. Internal temperature should be about 195–200°F (90–93°C) for ultra-tender slices.
Rest and slice: Remove the pork and rest for 10–15 minutes.
Slice across the grain into 1/4-inch (0.5 cm) pieces. Thicker slices are fine if you prefer a meatier bite.
Warm serving option: Keep slices moist by ladling a bit of hot broth over them or keeping them tented with foil.
Serve: Set out lettuce, perilla leaves, kimchi, ssamjang, chilies, and garlic slices. To eat, place pork on a leaf, add a dab of ssamjang and a bit of kimchi, wrap, and enjoy.