Preheat your air fryer to 360 degrees F (182°C) and then lay out a slice of bread on a clean surface or cutting board. Spread butter on one side of the slice of bread.
Place the slice of bread butter side up, on a plate or any clean surface.
Place a slice or two of cheddar cheese on top of another slice of bread, making sure you cover the entire surface of the slice. Season the cheese with a pinch of salt and black pepper (optional).
Place the buttered bread slice on top of the cheese, butter side up.
Place the sandwiches in the air fryer basket, butter side up, making sure they don't overlap. If your air fryer tends to stick, you can use cooking spray or line the air fryer basket with parchment paper.
Air fry the sandwiches at 360°F (182°C) for 4-5 minutes until the bottom side is golden brown and crispy.
Carefully flip the sandwiches with a spatula, and butter the slice. Make sure the parchment paper stays in place if you happen to be using one. Air fry for 3-5 minutes more until the second side is also golden brown and the cheese melts.
Remove the grilled cheese sandwiches from the air fryer and allow them to cool for a minute or two. After they cool, cut the sandwiches diagonally and serve them hot with a side of French fries, chips, or roasted tomato soup.