In a large mixing bowl combine the sugar and fish sauce, and mix until the sugar has dissolved. Add half of the lemongrass, half of the chile, half of the garlic and the chicken pieces. Coat the chicken, then let it marinate, covered, in the refrigerator for 1 hour or overnight for a better result.
Heat a large saucepan or wok over medium heat, add the oil and remaining lemongrass and cook for 1 minute. Then add the garlic, shallots, chile, and fry until fragrant and slightly brown.
Turn the heat to high, then add the chicken searing all sides until browned, about 2 minutes on each side.
Add the onions and coconut juice, and cover with a lid. Cook the mixture over medium heat for 5 minutes, or until the sauce has reduced by half. Remove the lid, add the scallions and cook 1 minute more.
Transfer the mixture to a bowl, garnish with coriander (cilantro) and eat with jasmine rice.