I should have known what I was getting into when I asked Diana Kennedy, the famously demanding author of nine landmark books on Mexican cooking, to teach me how to make a proper corn tortilla. I took cooking classes from her at Fonda San Miguel in 1980, when the petite English-born Kennedy commandeered the room like a headmistress. Thirty years later, we are back at Fonda—she is good friends with the owners and visits often from her home in central Mexico—and she is her same feisty self. As the kitchen crew scurries about, she lambasts the sorry state of today’s commercial tortillas with enormous zeal. “No flavor!” she exclaims. “Everybody is using packaged mixes!”

Everyone, that is, except Kennedy. Her corn tortillas start with—corn. She runs her fingers through a bowl of dried kernels. “Field corn,” she declares, “is much less sweet than corn you eat fresh.” With brisk motions, she shows how the kernels must be soaked with powdered calcium dioxide to loosen their outer skin, then ground and shaped into masa. Hefting a batch of the stuff onto the counter, she pinches off balls, flattens them with a tortilla press, and cooks them on a hot iron comal (“I do not like a thick comal,” she asserts). A minute later, I taste the results: My tortilla is soft yet toasty, and subtly earthy.

You’d expect no less from a person whose life’s purpose has been to chronicle for Americans (and Mexicans too) the richness and complexity of Mexico’s regional cuisines. This mission continues in her latest cookbook, the sumptuously illustrated, 459-page Oaxaca al Gusto: An Infinite Gastronomy (University of Texas Press). Any other 88-year-old author would consider such a work a career capper. But with Kennedy, you never know what’s next.