01 - Combine chicken pieces with fish sauce, soy sauce, brown sugar, black pepper, garlic, and shallot in a large bowl. Mix thoroughly to coat evenly. Marinate for at least 15 minutes, up to 1 hour for enhanced flavor penetration.
02 - Heat neutral oil in a large skillet or clay pot over medium heat. Add brown sugar and stir continuously until melted and transformed into deep amber caramel, approximately 2-3 minutes. Watch carefully to prevent burning.
03 - Add marinated chicken to the caramel, reserving excess marinade in the bowl. Sear for 3-4 minutes, turning pieces to ensure even coating with the caramelized sugar base.
04 - Pour in reserved marinade, water, fish sauce, soy sauce, and sliced chilies if using. Stir thoroughly to combine all elements and distribute seasoning evenly.
05 - Reduce heat to low, cover, and simmer for 25-30 minutes. Stir occasionally to prevent sticking and ensure even cooking. Continue until chicken is completely cooked through and sauce has thickened to a glossy consistency.
06 - Remove lid during the final 5 minutes of cooking to allow sauce reduction and concentrate flavors. The sauce should coat the chicken pieces generously.
07 - Scatter sliced scallions and fresh cilantro leaves over the dish. Serve immediately accompanied by steamed jasmine rice.