The quesadilla debate is a genuine cultural flashpoint: in Mexico City, a quesadilla is a folded tortilla filled with whatever you want (potato, mushroom, squash blossom, huitlacoche) and cheese is optional — you must specify 'con queso' if you want it. Everywhere else in Mexico, a quesadilla without cheese is a taco. The standard version uses a flour or corn tortilla folded over Oaxacan string cheese (quesillo) or Chihuahua cheese, griddled on a comal until the cheese melts and the tortilla develops golden patches. Street quesadillas are pressed flat on the comal; restaurant quesadillas may be assembled open-faced and broiled. The cheese choice matters: Oaxacan quesillo stretches when melted into the characteristic pull; Chihuahua cheese melts cleaner and crisper. Both are correct in different contexts.
In a skillet, heat the vegetable oil over medium heat.
Add the chopped onions and bell peppers, and cook until they are soft and slightly caramelized.
If using, add the cooked chicken, beef, or vegetables to the skillet and heat through.
Place one tortilla on a flat surface.
Sprinkle a layer of shredded cheese over half of the tortilla.
Add a portion of the cooked filling over the cheese.
Sprinkle a little more cheese on top of the filling.
Fold the tortilla in half to cover the filling.
Repeat with the remaining tortillas and filling.
Heat a clean skillet or griddle over medium heat.
Place a quesadilla in the skillet and cook for about 2-3 minutes on each side, or until the tortilla is golden brown and the cheese is melted.
Remove from the skillet and repeat with the remaining quesadillas.
Cut each quesadilla into wedges.
Griddled folded tortilla with melted cheese (Oaxacan or Chihuahua); Mexico City insists cheese is optional; everywhere else disagrees.
Mexico; colonial-era introduction of dairy merged with pre-existing tortilla culture; Mexico City street quesadilla developed as an urban form.
Flour or corn tortilla, Oaxacan quesillo or Chihuahua cheese; filling options: huitlacoche, flor de calabaza, rajas, black beans.
Press the quesadilla on a dry (ungreased) comal for the first minute — this toasts the tortilla before the cheese melts; add a tiny bit of oil in the last 30 seconds for crispness.
Salsa verde or roja, sliced jalapeño, crema; as a snack, starter, or light meal.