Step 1

Preheat the air fryer to 400 degrees F (200 degrees C).

Step 2

Cut grapefruit in half crosswise and slice off a thin sliver off the bottom of each half if the fruit isn't sitting flat. Use a sharp paring knife to cut around the outside edge of the grapefruit and between each segment to make the fruit easier to eat once cooked.

Step 3

Combine softened butter and 1 tablespoon brown sugar in a small bowl. Spread mixture over each grapefruit half. Sprinkle with remaining brown sugar.

Step 4

Cut aluminum foil into two 5-inch squares and place each grapefruit half on one square; fold up the edges to catch any juices. Set in the air fryer basket.

Step 5

Broil in the air fryer until sugar mixture is bubbling, 6 to 7 minutes. Sprinkle fruit with cinnamon before serving.