Heat the butter or oil in the saucepan.
Spread out a tortilla in the pan, add ¼ of the cheese over one half, and fold the other half over.
Repeat with another tortilla so that you have two folded tortillas side by side in the pan.
Toast for 30-45 seconds, flip them both, toast for another 30-45 seconds, remove, and repeat.
Cut each quesadilla into quarters and serve.