In a mixing bowl, combine the brown sugar and flour. Add the butter. Using your hands rub the butter into the sugar/flour mix until it’s the texture of very coarse cornmeal. Add cinnamon to taste.
Slice the apple into slices. You don't need to peel them. Then arrange them in a small pan that will fit into your air fryer without the apples hitting the top. Sprinkle the sugar/flour mixture on top of the fruit.
Put into your air fryer at 325 degrees for 9-13 minutes or until the top is brown.
Allow to cool for 5-10 minutes before digging in. This can be eaten hot, cold, or at room temperature whatever you love best.