01 - Combine chicken, soy sauce, vinegar, garlic, bay leaves, peppercorns, and brown sugar in a large bowl. Toss thoroughly to coat. Marinate for 30 minutes at minimum, or refrigerate overnight for deeper flavor penetration.
02 - Remove chicken from marinade and reserve the liquid. Pat chicken pieces completely dry with paper towels to ensure proper browning.
03 - Heat vegetable oil in a large deep skillet or Dutch oven over medium-high heat. Place chicken skin side down and sear until golden brown, approximately 2-3 minutes per side. Work in batches if necessary to avoid overcrowding.
04 - Add sliced onions to the pan and sauté for 2 minutes until softened and fragrant.
05 - Pour reserved marinade and water into the pan. Add quartered potatoes if using. Bring mixture to a gentle simmer.
06 - Cover pot, reduce heat to low, and cook for 25-30 minutes. Stir occasionally to ensure even cooking. Continue until chicken is completely tender and cooked through.
07 - Uncover the pot and continue simmering for 10-15 minutes. Allow sauce to reduce and thicken to desired consistency.
08 - Discard bay leaves and adjust seasoning if needed. Serve hot over steamed rice. Garnish with chopped scallions or crispy fried garlic if desired.