Place the butter in a large mug or small bowl; microwave until melted (about 20 seconds).
Add the egg, milk, syrup, vanilla extract, and cinnamon. Whisk with a fork until well blended.
Add the bread pieces and gently stir making sure the egg mixture is coated evenly throughout.
Microwave for 90 seconds and then check for doneness. Microwave in 20 second intervals after that. It takes about 2 minutes in my microwave, but you may have to experiment.
