Melt butter in a nonstick skillet over medium heat.
Place one tortilla flat in the skillet. Sprinkle the cheeses evenly across the surface, then top with the second tortilla.
Cook for 2–3 minutes, or until the bottom tortilla is golden and the cheese starts to melt. Carefully flip and cook for another 2–3 minutes.
Remove from the skillet and let cool for a minute. Slice into wedges and serve warm with salsa, sour cream, or guacamole.