01 - Combine chicken, soy sauce, vinegar, garlic, bay leaves, peppercorns, and brown sugar in a large bowl. Toss to coat thoroughly. Marinate for at least 30 minutes in the refrigerator, or 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 oil in a large, deep skillet or Dutch oven over medium-high heat. Add chicken pieces skin-side down and brown for 2 to 3 minutes per side. Work in batches if necessary to avoid overcrowding the pan.
04 - If using onions, add to the pan and sauté for 2 minutes until softened but not browned.
05 - Pour in the reserved marinade and water. Add potatoes if using. Bring to a simmer, then cover and reduce heat to low.
06 - Cook covered for 25 to 30 minutes, stirring occasionally, until chicken is tender and cooked through to an internal temperature of 165°F.
07 - Uncover and simmer for an additional 10 to 15 minutes to reduce and thicken the sauce until it reaches desired consistency. Discard bay leaves before serving.
08 - Adjust seasoning if necessary. Serve hot over steamed jasmine or white rice, garnished with chopped scallions or fried garlic if desired.