Leftovers are always better the next day. Or, in the case of Bangkok restaurant Wattana Panich, the next generation.

The giant pot of neua tune, a beef stew popular in the Thai capital, has been simmering since owner Nattapong Kaweenuntawong was a child, more than 45 years ago. Growing up studying the exact flavor profile of the stew from his father, Kaweenuntawong now balances the flavor himself daily. He employs an ancient practice called Hunter’s Stew or Perpetual Stew, using some of the previous day’s leftover broth to start the base of the following day’s soup. “We keep tasting. There is no recipe,” he told Channel News Asia.

A secret blend of spices and herbs, stewed beef, raw beef slices, meatballs, tripe, and other organs swim about the deeply bubbling vat. While new restaurants and high-end condominiums now dwarf the humble one-story bistro in Bangkok’s busy Ekamai neighborhood, the complex and rich flavor of Wattana Panich’s headline soup keeps the dish relevant and its followers loyal.