Carlos Figueroa is focusing intently on what he says was once just an avocation—freshly made, small-batch tortillas using heirloom corn varieties that are centuries, perhaps even thousands of years old. “I just wanted good corn tortillas, man,” explains the owner of Maiz Tucson, who began making his by hand seven years ago. His day job was at a health research lab in this southern Arizona city, which is the home of the University of Arizona. Tucson is also America’s first City of Gastronomy, a UNESCO distinction that signifies the area’s devotion to its food heritage. “These heritage foods are representative of many living traditions that thrive today, and are a source of identity and cultural vitality for the people who live here,” explains the City of Gastronomy citation. “We call it the Tucson terroir,” said Devon Sanner, a local chef, advocate for the 2016 UNESCO designation, and cofounder of Zio …