Heat the Blackstone to medium (or set a large skillet over medium heat).
Add the butter and let it melt.
Arrange the apple slices in a single layer and cook, stirring and flipping occasionally until they are just softened, about 7 minutes.
Sprinkle with apple pie spice and cook 30 seconds longer. Move the apple slices to a cool part of the griddle. If using a skillet, transfer them to a bowl.
Spread the butterscotch sauce all over one side of the tortilla. This acts as the "glue".
Mound the apples on one half of the tortilla. Fold it over to create a half-moon shape.
Cook over medium heat, flipping once, until the tortilla is golden brown and beginning to crisp, about 2 minutes per side.
Remove from the heat and let cool for 5 minutes before slicing.
Notes
Let it cool--Let your quesadilla cool for 5 minutes before slicing. It will be hot, and the cooling time will also help everything to stick together.
Slicing your quesadilla--For easy slicing, use a pizza cutter!
Don't forget the napkins--These can be a little messy to eat, so have a napkin handy.