In a mixing bowl, combine lemongrass, shallots, garlic, ginger, oyster sauce, soy sauce, fish sauce, honey, brown sugar, and neutral oil. Mix well.
Add the chicken thighs and coat them thoroughly in the marinade. Cover and refrigerate for at least 1 hour, preferably overnight for maximum flavor.
In a small bowl, dissolve sugar in warm water. Stir in fish sauce and lime juice. Add minced garlic and chili. Taste and adjust: add more lime for tartness, add more sugar for sweetness, add more chili if you like it spicy. Set aside.
Heat a large skillet or grill pan over medium heat. Lightly oil the pan if needed. Place the marinated chicken thighs smooth-side down. Cook for 5–6 minutes on the first side until caramelized and golden. Flip and cook the other side for another 5–6 minutes, or until cooked through and slightly charred around the edges. For best results, spoon some leftover marinade over the chicken in the final minute of cooking to enhance the glaze.
Let the chicken rest for 2–3 minutes, then slice or serve whole. Serve over steamed jasmine rice, pickled vegetables, or cucumber slices. Drizzle with nước chấm or serve it on the side for dipping.
