Preheat a cast iron or stainless steel skillet on medium heat with your oil of choice.
Dice onions into pieces no bigger than a half inch square.
Once the skillet is preheated, add the onions and reduce the heat to medium low to caramelize. Gently sauté the onions until translucent and light brown. Be sure to stir the onions occasionally.
When the onions are caramelized, remove them from the skillet and set aside.
Preheat your cast iron pizza pan or skillet on the stovetop on a medium heat.
While the pan is preheating, assemble your quesadillas on your counter. For each tortilla, mix together ½ cup shredded cheese with ½ cup Shredded beef 1 TBSP caramelized onions.
Once mixed, evenly distribute the mixture onto half of the tortilla. Fold the other half over the filling to make a half circle. Repeat this for all the tortillas and mixture you have.
When the cast iron is heated, transfer one tortillas to the cast iron pan and cook each side until golden brown. Repeat for each prepared quesadilla.
As each quesadilla is finished cooking, you can serve immediately. If you are waiting to serve everyone at once, I recommend transferring each finished quesadilla to a cooling rack. This will ensure the outside of the tortilla stays crispy!
After all quesadillas are cooked to your preference, serve immediately with your desired sides.
Store any leftovers into an airtight container and in the fridge for 3-5 days.