No one can agree on the enigmatic background of Thailand’s well-known tom yum soup. Some claim it was invented by the royal chefs of the Ayutthaya kingdom to highlight the region’s exceptional local cuisine, and others claim it was invented by a Thai boatman who, while traveling to China for business, mixed lemongrass, lime leaves, and shrimp paste into a hot-boiled pot of soup. It has been around since at least the 14th century. Some continue to refer to it as a dish prepared by farmers in rural areas that is infused with spices and herbs. No matter where it came from, it is now a mainstay of Thai cooking, and this recipe for a therapeutic broth.