Place one tortilla on your work surface. Sprinkle cheese evenly over the surface, leaving about a 1/2-inch border.
If using any fillings, layer them over the cheese now.
Heat a nonstick or cast iron skillet over medium heat. No butter or oil needed.
Carefully transfer the tortilla (cheese side up) to the skillet. If you’re making a cheese-only quesadilla, cover with a lid and cook for 2–3 minutes, or until the bottom is golden and the cheese is melted. If you’ve added other fillings, skip the lid to prevent steam from making the tortilla soggy.
Place the second tortilla on top and gently press down. Use a spatula to flip the quesadilla, and cook uncovered for another 2–3 minutes, until the second side is golden and crisp.
Transfer to a cutting board. Let rest for 1 minute, then slice into wedges and serve warm with your favorite dips.