Heat large griddle over medium heat. Grease surface with butter.
In shallow flat dish, combine eggs, heavy cream, Grand Marnier, cinnamon and orange zest.
Soak each piece of bread in the liquid for at least 30 seconds each side. Shake off any excess and transfer to griddle. Cook until golden brown, about 5 minutes on each side, flipping only once.
Serve hot with pure maple syrup or a dusting of powdered sugar.