In Thai, this is called Gai Tom Kha. Be sure to use unsweetened coconut milk, which is available in Asian markets. IN A SAUCEPAN, bring the coconut milk, chicken stock, galangal and lemon grass to a boil; reduce and simmer for 20 minutes. Strain stock; discard galangal and lemon grass. Return stock to a boil, add chicken and reduce to a simmer until tender (about 2 minutes). Add fish sauce, citrus leaves and chiles. Stir in lime juice. Garnish with more chiles to taste and coriander leaves. Serve hot.