The oval shape is meant to echo the pre-Hispanic original almost exactly, and archaeologists have found evidence that a nearly identical stuffed masa cake was eaten in the Valley of Mexico centuries before the Spanish arrived.
Blue or white corn masa is stuffed with mashed fava beans, beans, or requesón cheese, shaped into a thick oval, and griddled until the outside crisps, then topped with nopales, salsa, cheese, and onion. Market griddle stalls across Mexico City and the surrounding valley cook them fresh to order.