Cut the chicken thighs and lemongrass into bite-sized pieces. Thinly slice the galangal and chili. Pound the shallot, lemongrass, and coriander roots just enough to release their juices.
Place a soup pot over medium-high heat. Pour 3 cups of water and add lemongrass, galangal, shallot, coriander root, and kaffir lime leaves to the boiling water. Let the herbs simmer for about 5 minutes until they become fragrant.