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, 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. Add chicken pieces skin-side down and brown for 2-3 minutes per side until golden. Work in batches if necessary to avoid overcrowding.
04 - Add sliced onion to the pot and sauté for 2 minutes until softened and fragrant.
05 - Pour reserved marinade and water into the pot. Add potatoes if using. Bring to a simmer over medium heat.
06 - Cover pot, reduce heat to low, and cook for 25-30 minutes. Stir occasionally to ensure even cooking. Chicken is done when meat pulls easily from bone and internal temperature reaches 165°F.
07 - Uncover pot and continue simmering for 10-15 minutes. Sauce will reduce and thicken to a glossy consistency. Adjust cooking time based on desired sauce thickness.
08 - Taste and adjust seasoning if needed. Remove and discard bay leaves. Serve hot over steamed jasmine rice. Garnish with chopped scallions or crispy fried garlic if desired.