1Bring the stock to a boil over medium heat in a soup pot. Add the lime leaves, chiles, garlic, ginger and lemongrass. Lower the heat to medium-low; cover the pot and gently simmer to let the spices infuse the broth, about 10 minutes.
3Uncover the pot and stir in the chicken, coconut milk, mushrooms, fish sauce, sugar and lime juice. Simmer to heat the chicken through, about 5 minutes. Sprinkle with salt and pepper.
5Garnish with the cilantro or chiles.