From page 31 of Oaxaca Tips
Itanoní $ 
Belisario Dominguez 513, Colonia Reforma 
Mon-Sat: 7AM-6PM; Sun: 8AM-2PM. Cash only.

This no-frills café, named for the Mixtec corn flower makes the best tortillas in town using only Oaxacan maíz criollo (native or "heirloom" corns) grown by small family producers. The limed corn is ground into masa (dough) on a metate (stone mortar) and the tortillas are pressed by hand and cooked on a comal (clay griddle). If the only tortillas you have ever tasted are those bland, limp things cranked out by machine from reconstituted masa harina (produced from cheap, imported American corn) and your chances of being invited to a village fiesta meal are slim to none, hie thee to Itanoní for a delectable lunch of tacos or quesadillas or other antojitos made with "real" tortillas.