Preheat the air fryer to 375°F (190°C) for 3–4 minutes. A warm basket helps the tortilla crisp quickly.
Prep the tortillas: Lightly brush or spray one side of each tortilla with butter or oil.
This side will face out for maximum crunch.
Assemble: Place one tortilla oiled side down on a plate or cutting board. Sprinkle the cheese evenly to the edges, leaving a small 1/4-inch border. Add any optional toppings in a thin layer.
Top with the second tortilla, oiled side up. Press gently to seal.
Air fry: Place the quesadilla in the basket. If your air fryer has strong airflow that can lift the top tortilla, weigh it down with a small, oven-safe rack or a few toothpicks (insert flat, parallel to the surface).
Cook for 5–7 minutes, flipping halfway, until the tortilla is golden and crisp and the cheese is fully melted.
Check and finish: If it needs more color, add 1–2 minutes. If the edges brown too fast, lower to 350°F (175°C) for the last minute.
Rest and slice: Let it sit for 1 minute to set the cheese. Slice into wedges and serve with your favorite dips.