National Mexican tradition — the masa quesadilla is pre-Columbian; the tortilla quesadilla is a 20th century evolution
Quesadillas are one of the most misrepresented dishes in Mexican cooking outside Mexico — internationally assumed to always contain cheese, but in Mexico City quesadillas are often defined by the comal-cooked masa dough filled with meat, vegetables, or cheese. Two versions: masa quesadilla (fresh corn masa patted flat, filled, sealed, and cooked on a comal — traditional) and tortilla quesadilla (flour or corn tortilla folded over cheese and heated in a pan — the modern mainstream version). Both are legitimate.
The filling defines the flavour — the quesadilla is the vehicle; cheese is one option among many
{"Masa quesadilla: press fresh masa flat (3–4mm), place filling in centre, fold and seal edges, cook on comal","Tortilla quesadilla: heat tortilla on comal, add cheese and filling, fold in half, press and flip until cheese melts","Quesillo (Oaxacan string cheese) or Chihuahua cheese are the canonical melting cheeses — not mozzarella","For masa quesadillas: comal must be at medium heat — too hot chars the exterior before the masa cooks through","Epazote is the traditional herb in masa quesadillas — added with the cheese before sealing"}
{"For masa quesadillas: press between two sheets of plastic (tortilla press works) — more even thickness than hand-patting","The comal-cooked masa quesadilla has a different texture than the tortilla version — slightly chewier exterior, more masa flavour","Mexico City quesadillas are frequently filled with huitlacoche (corn fungus), flor de calabaza (squash blossom), or rajas — not just cheese","For restaurants: masa quesadillas made to order; tortilla quesadillas can be pre-assembled and stored briefly"}
{"Adding cheese to corn tortilla quesadillas and expecting melt — corn tortilla does not conduct heat as evenly as flour for cheese melting","Over-filling — the quesadilla must seal completely to prevent filling escaping onto the comal","Using mozzarella — the moisture level and flavour are wrong for Mexican quesadillas","Cooking at high heat — burns the exterior before the interior melts and cooks through"}
My Mexico City Kitchen — Gabriela Cámara; The Art of Mexican Cooking — Diana Kennedy