This step is optional, but if using regular pepperoni, it helps reduce grease and mess. Place a paper towel on a microwave-safe plate, arrange the pepperoni in a single layer on top, and microwave for 20 to 30 seconds. This process slightly cooks the pepperoni, melts some of the fat, and allows it to be absorbed by the paper towel.

Spread a thin, even layer of tomato sauce over the entire tortilla. Arrange the pepperoni slices on one half of the tortilla. Sprinkle a generous layer of cheese over the pepperoni, then fold the other half of the tortilla over to cover the filling.

Melt a small amount of butter in a skillet over medium heat. Place two quesadillas in the skillet and cook for 2 to 3 minutes, or until lightly browned. While the first side cooks, lightly butter the top of each tortilla. Flip them over and cook until the second side is golden brown.

Remove the quesadillas from the pan and let them rest for a couple of minutes before slicing them into quarters or thirds. If desired, serve with warm pasta sauce for dipping.