Cut sticks. Slice each bread piece into 4 sticks roughly ¾ inch wide.
Whisk custard. In a shallow bowl, whisk eggs until smooth. Add milk, cream, brown sugar, vanilla, cinnamon, nutmeg, and salt. Whisk until uniform.
Preheat air fryer to 350°F for 3 minutes. (350°F, not higher — that's the fluffy temperature.)
Soak the sticks. Place each stick in the custard for 15 seconds per side. Let excess drip off.
Arrange in basket. Lightly grease basket or line with parchment. Arrange sticks in a single layer with space between.
Cook side one. Air fry at 350°F for 4 minutes.
Brush and flip. Brush tops with melted butter. Flip with tongs. Brush the other side.
Cook side two. Air fry another 3–4 minutes until lightly golden outside and soft inside.
Finish. Toss in cinnamon sugar if using. Dust with powdered sugar and serve immediately with maple syrup.