For a richer flavor, consider using brown butter instead of regular butter. Simply melt the butter in a saucepan over medium heat, swirling occasionally, until it turns a nutty brown color. Let it cool slightly before using. The cooking time may vary slightly depending on your air fryer model. Keep a close eye on the donut holes and adjust the time as needed. For a more intense lemon flavor, add a pinch of lemon zest to the glaze. These donut holes are best enjoyed warm. Store any leftovers in an airtight container at room temperature for up to 2 days.