Coat a well-seasoned cast-iron pan (you can use a nonstick pan if you’re feeling timid) with the oil, wiping out the excess with a paper towel, and warm the pan over medium-high heat. Add a tortilla to the pan and toast until just beginning to brown, about 2 minutes, then remove and reserve. Add half of the cheese to the pan, sprinkling it evenly to make a circle just slightly larger in diameter than the tortilla. Carefully place the toasted tortilla on top of the cheese toasted side down, centering it. Spread the remaining cheese over the tortilla, then place the second tortilla on top of the cheese. When the cheese has browned, after about 4 minutes, using a small metal spatula, carefully peel up an edge to get underneath. Once you have lifted up an edge, it should be easy to peel up the entire crispy mass with the spatula. Then, working carefully, flip the whole thing over to toast the second tortilla and melt the cheese in the interior. This should take about 3 minutes. Serve the quesadilla piping hot with whatever accompaniments— salsa, sour cream, guacamole, hot sauce—you like.