Aside from boneless skinless chicken thighs, fresh Thai chile peppers, and southern Thai curry paste, Punchfork lists a few other ingredients, namely, vegetable oil, sugar, fish sauce, lemongrass, and makrut lime leaves (fresh or frozen will work).
As previously mentioned, khua kling gài is spicy, well-balanced, and fresh, but why is this so? Well, the spice levels have already been discussed, but the “well-balanced” aspect comes from the fish sauce and sugar. Fish sauce, as explained by Lacademie, is fishy, umami, and salty, while sugar is, of course, sweet. So far, the dish sounds like a party in the mouth with spicy, sweet, salty, and savory flavors.
Serious Eats notes that the fresh and herbal flavors of khua kling gài is due to the lemongrass, makrut lime leaves, and fresh Thai chiles. Foodiosity describes lemongrass as “citrusy” with a “strong vegetal, earthy flavor” that bears some small resemblances to lemons. Makrut lime leaves, aka, kaffir lime leaves, come from kaffir limes, which are found in some parts of southeast Asia and southern China, per US Citrus. It has a “bright citrus flavor” and is very aromatic, enhancing cuisines across Malaysia, Indonesia, Vietnam, and Thailand alike. So not only does khua kling gài have elements of freshness and herbaceousness, but citrus and earthy flavors as well.