Heat skillet over medium heat. Add butter. Place a tortilla in the pan, heat for a few seconds and turn over. Sprinkle the cheese evenly over the tortilla. Add the other ingredients on top of the cheese to one half of the tortilla. fold over the other half. The quesadilla now looks like an omelette. Turn the burner down and cook for a couple of minutes. Carefully turn over and cook on the other side until the cheese is melted. It should be lightly browned on both sides. Cut into three wedges.