01 - Combine chicken pieces with fish sauce, soy sauce, brown sugar, black pepper, garlic, and shallot in a large bowl. Mix thoroughly and marinate for at least 15 minutes, up to 1 hour for deeper flavor penetration.
02 - Heat oil in a large skillet or clay pot over medium heat. Add 2 tbsp brown sugar and cook, stirring constantly, until sugar melts and turns a deep amber caramel color, approximately 2–3 minutes.
03 - Immediately add marinated chicken, reserving excess marinade liquid. Sear for 3–4 minutes, turning pieces to coat evenly in the caramelized sugar.
04 - Pour in reserved marinade, water, fish sauce, soy sauce, and sliced chilies if using. Stir well to combine all ingredients.
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 fully cooked and sauce has thickened to a glossy consistency.
06 - Remove lid during the final 5 minutes of cooking to allow sauce to reduce further if needed, concentrating flavors.
07 - Top with thinly sliced scallions and fresh cilantro leaves. Serve immediately alongside steamed jasmine rice.