Chicken soup is the tonic that soothes all wounds, from a light sniffle to an emaciated IPO. And yet ordering chicken soup at a great restaurant seems a bit like going to a cocktail haven and ordering a tall rocks glass full of the city’s finest tap water.

For all its cockles-warming charms, chicken soup is a simpleton bore of a dish. That is, unless you’re in a Thai restaurant. Thai cuisine’s version of chicken soup is tom kha gai, and it’s wondrous. The literal translation is “chicken galangal soup,” but …