Spread half the butter on one side of each tortilla.
Put one tortilla, butter side down in the hot pan. Sprinkle the cheeses
evenly onto the center of the tortilla in the pan - but not all the way to
the edges.
Put the tomato, onion, bacon and jalapeño over the cheese, and cover
with the other tortilla butter side up (like a grilled cheese sandwich).
When the bottom side is browned, about 45-90 seconds, flip the quesadilla
and grill the other side.
Remove the quesadilla from the pan and, using a pizza cutter, cut through
the middle like a pizza.