Spay the ramekins with cooking spray or brush them with olive oil.
Whisk together one large egg, milk, and a splash of vanilla extract in a small bowl. If desired, you can also add a pinch of cinnamon, salt, or black pepper to the mixture for extra flavor.
Place the bread into the french toast batter, and leave for about one minute, until the bread has soaked up the batter.
Place the bread into the bottom of the sprayed ramekins or mug. Crack an egg into the center of the bread. Season with ground cinnamon, or add shredded cheese.
Place the mug or ramekin into the air fryer. Cook at 330 degrees F, with a cook time of 5-7 minutes or until the French toast is golden brown and crispy on the outside. Make sure to check the French toast halfway through cooking and gently toss or stir the cubes to ensure even browning.
Garnish with additional shredded cheese, or sprinkle ground cinnamon on top!