Prepare the filling: In a bowl, mix the shredded cheese with optional ingredients like cilantro, onions, or jalapeño if using.

Heat the skillet: Place a large skillet or griddle over medium heat and let it warm up for about 2 minutes.

Butter the tortilla: Lightly butter one side of each tortilla. This will help it crisp up and turn golden brown.

Assemble the quesadilla: Place one tortilla butter-side down in the skillet. Sprinkle a generous amount of cheese mixture evenly over the tortilla.

Add the top tortilla: Place another tortilla on top, butter-side up. Press down gently with a spatula.

Cook until golden: Cook for about 2-3 minutes per side, or until the tortilla is crispy and golden and the cheese is fully melted.

Flip carefully: Use a large spatula to flip the quesadilla to the other side. Cook for another 2-3 minutes.

Slice and serve: Transfer to a cutting board, let it cool for a minute, then slice into wedges. Serve with salsa, sour cream, or guacamole.