Whisk together the egg, milk, sugar, salt and cinnamon. Pour into a shallow pan (I used an 9" x 11" baking dish).
Add the bread slices. Refrigerate for 4 hours. Optionally, flip after 2 hours (carefully! the bread may be very soft and want to fall apart).
Heat up your Griddler using the griddle plates. Set the Griddle dial to 425 F and the Selector to Griddle. Open the Griddler with the plates flat, side-by-side.
Once the griddles are hot place 1 tablespoon of butter on each griddle plate. Using a nylon brush or heat proof spatula, spread the butter out evenly. You don't want the bread to stick.
Add 2 slices of the bread to each griddle plate.
Cook for 5-10 minutes per side. Cook time is going to depend on how thick your bread is and how you like your bread done. This recipe produces a moist, soft French toast. If you like yours to have a bit of a crust you will have to cook the bread longer. Be careful flipping the bread
When the bread is done to your liking remove and serve with your favorite toppings.