Fry the pepperoni in a 12 skillet over medium heat for about 5 minutes or until browned.
Remove from skillet.
Wash and dry the skillet.
Spread refried beans over 4 tortillas on 1 or 2 baking sheets.
Sprinkle with onion and half the shredded cheese.
Sprinkle with the pepperoni slices and the remaining shredded cheese.
Top each stack with a tortilla.
Preheat the skillet over medium heat.
Heat each quesadilla in the skillet for 3 to 5 minutes or until golden brown and cheese is melted.
Remove to warmed serving plates.
Keep warm until served.
Cut each quesadilla into 4 wedges and serve with sour cream and salsa.