Preheat the air fryer to 180°C (350°F) and set the timer to 10 minutes.
In a small bowl, mix together the mayonnaise, dijon mustard, and garlic powder until well combined. Take two slices of bread and spread a thin layer of the mayo mixture on one side of each slice. This will be the side that faces inward and touches the cheese.
1 tablespoon Mayo, ½ teaspoon Dijon Mustard, ¼ teaspoon Garlic Powder, 2 Slices Bread
Flip the bread slices over and spread a thin layer of butter on the other side of each slice. This will help create a crispy and golden exterior.
1 tablespoon Butter
Flip one slice of bread back over (so the mayo is facing you) and pile on the grated cheese.
50 g Mature Cheddar
Place the other slice of bread on top, butter side up, so that the mayo side of the bread is touching the grated cheese.
Air fry at 180℃ (350°F) for 6 mins. Flip with tongs or a plastic spatula then air fry for a further 4 minutes until golden and crispy.