Add the eggs, milk, vanilla, and cinnamon to a wide, shallow bowl. Mix with a fork or a small whisk.
Dip each piece of bread into the egg mixture, turning over with a fork to coat all sides.
Coat the tray of the air fryer with nonstick spray. Place the French toast on top.
Preheat the air fryer to 350 degrees F. When it comes to temperature, add the tray with the French toast. Cook for 3-4 minutes without flipping, until just golden brown.
Remove, brush with melted butter (optional), and serve with maple syrup or another desired dip like applesauce or yogurt.
Notes
Store leftovers in an airtight storage container in the fridge for up to 5 days or place into a freezer bag and remove as much air as possible. Freeze for up to 6 months. Pop into the toaster (from the fridge or freezer) to warm through, or you can warm up on a heat-safe plate in 15- to 30-second increments in the microwave.
Banana French Toast Sticks: Replace 1 egg with 1/4 cup mashed ripe banana.
Apple French Toast Sticks: Replace 1 egg with 1/4 cup applesauce.
Pumpkin French Toast Sticks: Replace 1 egg with 1/4 cup pumpkin puree. Add a little more milk if the batter seems very thick.
Cinnamon-Sugar French Toast Sticks: Stir together 1 tablespoon sugar and 1 teaspoon cinnamon in a small bowl. Sprinkle over sticks as soon as they're finished cooking.
Egg-free: Use the banana or apple version above and use 1/2 cup of either to replace the eggs.