Tom kha kai, tom kha gai or Thai coconut soup (Thai: ต้มข่าไก่, tom kha kai; Lao: ຕົ້ມຂ່າໄກ່, tom kha kai, literally “chicken galangal soup”) is a spicy and sour hot soup with coconut milk in Thai and Lao cuisines.
In Thailand, most tom kha kai recipes typically include coconut milk, galangal, kaffir lime leaves, lemongrass, Thai chilli peppers, coriander (or dill weed), straw mushrooms (or other mushrooms such as shiitake), chicken, fish sauce, and lime juice. Fried chillies are sometimes added.
In a Thai-style tom kha kai, dill weed is not used, whereas in a Lao-style tom kha kai, dill weed (phak si, Lao: ຜັກຊີ) is used. Dill weed is a common herb which is used in Lao cuisine. The Thais’ answer to dill weed (known in Thailand as phak chi Lao (Thai: ผักชีลาว), since it is known locally as a Lao herb) in Thai tom kha is coriander or cilantro (phak chi, Thai: ผักชี).
There are other versions of tom kha kai made with seafood (tom kha thale, Thai: ต้มข่าทะเล), mushrooms (tom kha het, Thai: ต้มข่าเห็ด), pork (tom kha mu, Thai: ต้มข่าหมู) and tofu (tom kha taohu, Thai: ต้มข่าเต้าหู้).
In the late 19th century, tom kha was not a soup. it was a dish of chicken or duck simmered in a light coconut broth with a generous amount of galangal. It was then served with a basic roasted chilli jam as a dipping relish.