01 - Set air fryer to 375°F and preheat for 3 minutes.
02 - Spread softened butter evenly on one side of every bread slice.
03 - Place two bread slices, buttered side down, on a clean surface. Layer two cheese slices on each. Add optional tomatoes, caramelized onions, or bacon if desired.
04 - Top with remaining bread slices, buttered side up, to complete the sandwiches.
05 - Arrange sandwiches in a single layer in the air fryer basket. Cook in batches if necessary.
06 - Air fry for 4 minutes. Carefully flip sandwiches, then air fry for an additional 3 to 4 minutes until bread is golden and cheese is melted.
07 - Remove sandwiches and let rest for 1 to 2 minutes. Slice as preferred and serve hot.