Add the pork belly chunks to a saucepan and fill it with water until the meat is just covered. Bring to a rolling boil over medium-high heat and cook for 5 minutes. Remove the pork from the saucepan, rinse with water, and drain. Pat dry with paper towels and set aside.
Heat a heavy-bottomed pot (or skillet) over medium-high heat. Transfer the pork belly to the pot and sear the meat for 1 minute on each side. Use tongs to flip the meat until each side is lightly golden brown and the oil is released.
Stir in the ginger, scallion, and garlic, and cook until fragrant, about 2 minutes. Add the rock sugar, star anise, bay leaves, light soy sauce, dark soy sauce, and sake. Stir well to coat the meat evenly with the sauce. Pour in 1 1/2 cups of hot water, or enough to just cover the meat, and bring to a boil over high heat.
Reduce the heat to medium-low and bring the mixture to a gentle simmer. Cover and braise the pork for 45 minutes, or until fork-tender and the sauce has reduced to a glossy coating without excess liquid. Stir every 10 minutes to prevent burning.
Serve immediately, garnished with finely sliced scallions on top.