Prepare griddle: Heat large griddle over medium heat. Grease surface with butter.
Prepare soak: In shallow flat dish, combine eggs, heavy cream, Grand Marnier, cinnamon and orange zest.
Soak bread: Soak both sides of each piece of bread in the liquid. Gently shake off any excess and transfer to griddle. Note: Due to the softness of the bread, do not soak until you are ready to directly transfer it to the hot griddle.
Cook French toast: 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.