WHEN CHEF ENRIQUE OLVERA OPENED his restaurant, Pujol, 13 years ago, his only goal was to serve "solid, tasty food" and be "the best restaurant in the neighborhood," he says. But that neighborhood was Mexico City's Polanco, the dining epicenter for a city of 8.5 million, and Olvera's budget was so small that his wife had to paint the walls. Since then, Pujol has far surpassed its initial aims: It's now widely thought of as Mexico's finest restaurant—and the 36th best in the world, according to the much-scrutinized S. Pellegrino rankings; and Olvera, who trained at New York's Culinary Institute of...