Quick: How many Mexican taco fillings can you name off the top of your head? Four? Five? In reality, there are dozens of taco fillings to be found all across Mexico, using just about every part of just about every animal (and that’s not to mention the vegetarian ones). Here are 20.
A taco, by definition, is a tortilla folded or rolled around (or just sitting beneath) a filling — a broad definition which opens the door to an infinite amount of taco possibilities. But in Mexico, traditional tacos tend to fall into a handful of styles: Tacos de asador (filled with meats that have been griddled or grilled), tacos de cazo (filled with meat slow-cooked in lard), and tacos de cazuela (braised or simmered meats). You’ll also occasionally find flautas, also called taquitos (in which the filled tortillas are rolled and deep-fried), or tacos sudados (“sweaty tacos,” in which tortillas are filled with meat and kept warm in a cloth-covered basket). Notice that hard-shell tacos, apart from flautas, aren’t generally a part of the Mexican taco lexicon.
We’re just discussing meat-based fillings today, but vegetarians shouldn’t despair. There are plenty of vegetable-based tacos to be found in Mexico as well, including those made with nopales (cactus pads), potatoes, rajas (roasted poblano pepper strips), squash blossoms, and huitlacoche (corn smut, a fungus that grows on corn, sometimes called "the truffle of Mexico").
Traditional tacos tend to be made with a double-layer of corn tortillas for extra support, with the fillings topped with diced onions and cilantro and sometimes a squirt of salsa or guacamole. As for lettuce, tomato, and shredded cheese? Again, not really a part of the Mexican taco lexicon.
Read on to learn all about the wide, wide world of Mexican taco fillings. Some of these you’ve most likely had (and can find variations of at your local Chipotle), others you’ve probably never heard of, and some are definitely not for the squeamish. But now, when you next happen upon a taco truck and someone asks you what exactly "sesos" is, you can tell them that they probably don’t want to know.
“Shepherd style” — thin slices of pork marinated in adobo and then stacked and pressed together on a vertical rotisserie, like those used to cook gyro meat or shawarma. The meat is carved off to order and mixed with pineapple, often cooked on the same spit.