01 - Combine chicken, soy sauce, vinegar, garlic, bay leaves, peppercorns, and brown sugar in a large bowl. Toss to coat well. Marinate for at least 30 minutes, or up to overnight in the refrigerator for deeper flavor.
02 - Remove chicken from marinade and reserve the marinade. Pat chicken pieces dry with paper towels.
03 - Heat oil in a large, deep skillet or Dutch oven over medium-high heat. Add chicken pieces skin side down and lightly brown on both sides, about 2-3 minutes per side. Work in batches if needed.
04 - Add onion to the skillet and sauté for 2 minutes until slightly softened.
05 - Pour in the reserved marinade and water. Add potatoes if using. Bring to a simmer.
06 - Cover, reduce heat to low, and cook for 25-30 minutes, stirring occasionally, until chicken is tender and cooked through.
07 - Uncover and simmer for another 10-15 minutes to reduce and thicken the sauce to your desired consistency.
08 - Adjust seasoning if necessary. Discard bay leaves. Serve hot with steamed rice, garnished with scallions or fried garlic if desired.