Many people's only experience with quesadillas has come in the drive-thru lane at their local Taco Bell. While these "quesadillas" are technically edible, they do not compare with the homestyle versions I enjoyed during my 5 year stay in Texas. Quesadillas are essentially the grilled cheese of Mexican cooking, and the simplest quesadilla is made using just cheese and a tortilla.
However, just like a grilled cheese, you can also add meats and veggies to make the flavor suit your tastes. Just about anything can be used as a filling. I like to use leftover fajita meat, along with the onions and peppers, for a quick lunch the next day. Another of my favorites is using leftover barbecue brisket. You can even make a vegetarian version with sauteed mushrooms, black beans, and spinach for the filling. The possibilities are really up to you.
The key to a good quesadilla is the pan. Cast iron is probably the best choice, but any heavy bottomed pan that distributes heat evenly will work. Just be sure not to turn the heat up too high, or you will burn the tortilla before the cheese melts. Also, if you kept the heat low, the cheese should melt enough to hold the quesadilla together when flipping it over.
4 burrito size tortillas
2 cups shredded cheddar cheese
1-2 cups filling (your choice)
3 Tbsp butter