Place the bacon strips in your air fryer basket in a single, non-overlapping layer. Set the temperature to 375°F (190°C) and cook for about 5-7 minutes or until they reach your desired crispiness. Transfer the cooked bacon to paper towels to absorb excess grease.

Generously butter one side of each slice of bread. Place two slices, butter-side down, into the air fryer basket. Layer on the cheese, followed by the crispy bacon, and any optional toppings you choose. Finish with the remaining slices of bread, ensuring that they are butter-side up.

Set the air fryer to 350°F (175°C) and cook for about 3-4 minutes. Carefully flip the toasties using a spatula, and continue cooking for another 2-3 minutes until they turn golden brown and the cheese is melted. Allow them to cool for about one minute before slicing diagonally for that classic toastie look.