Tom Yum Kung — Classic Prawn Hot-Sour Soup / ต้มยำกุ้ง

Central Thai — though versions of the hot-sour prawn soup appear throughout Thailand, the Central Thai version with galangal-lemongrass-kaffir lime leaf is the canonical form

Tom yum kung is the most internationally recognised Thai soup and consequently the most frequently mis-executed. The broth is hot-sour-aromatic, not creamy — 'tom yum nam khon' (creamy, with evaporated milk or coconut milk) is a variation, not the original. The base is a clear broth built by simmering galangal, lemongrass, kaffir lime leaves, and sometimes crushed chilli in pork or chicken stock until fragrant, then seasoning aggressively with fish sauce and fresh lime juice added off heat. The prawns (or mushrooms, tofu, or mixed seafood) go in at the last moment. The critical rule: lime juice is added after the pot is off the heat — boiled lime juice becomes bitter and loses its fragrance.

• Vietnamese canh chua (sour soup) uses a similar acidic broth with fish but adds pineapple and bean sprouts; Cambodian samlar m'chu kreung uses a similar herb infusion base; the hot-sour principle appears in Lao tom khem.

Tom yum's sensory impact is immediate and multi-dimensional: the lime hits the sides of the mouth, the chilli warms the back of the throat, the galangal provides a piney top note, and the fish sauce binds everything into a coherent broth. The prawn is almost incidental to the flavour architecture.