Add 4 tablespoons unsalted butter to a medium ramekin and place in your air fryer basket. Heat air fryer to 400°F. Allow butter to melt for 3 to 4 minutes. Carefully remove ramekin using oven mitts (it’ll be very hot), and set aside to allow the butter to cool for a few minutes. Alternatively, melt butter in the microwave in 30-second intervals.
Meanwhile, finely grate the zest of 1 small orange until you have 2 teaspoons zest.
In a medium shallow bowl (large enough to fit 4 slices of bread), whisk together 2 tablespoons cornstarch, 2 tablespoons powdered sugar, 1 teaspoon cinnamon, and a pinch of kosher salt.
Crack 4 large eggs into the bowl and beat the dry ingredients into the beaten eggs, using the whisk to scrape any powder from the edges. Whisk in 2/3 cup half-and-half, 1 teaspoon vanilla extract, the orange zest, and the melted butter.
Lightly coat the air fryer basket with cooking spray. If your basket is not big enough to hold 4 slices of bread in a single layer, dip 2 slices in the egg mixture, soaking both sides. If your basket is bigger, work with all 4 slices at a time. Shake off any excess mixture and add to the air fryer basket.
Cook for 4 minutes. Flip toasts and cook until golden and crispy on both sides, 3 to 6 minutes more. If necessary, tent 2 slices cooked French toast with foil to keep warm, then dip remaining 2 slices of bread and repeat cooking process.
Using a fine-mesh strainer, dust powdered sugar on top of French toast. Serve immediately with desired toppings.