Mix together the egg, milk, vanilla, cinnamon, brown sugar, and pinch of salt to form the liquid custard. (I like to reserve a little cinnamon and brown sugar to sprinkle on the toast slices just prior to grilling as well.)
Dip the thick bread slices in the custard to ensure each piece is evenly coated, allowing the excess liquid to drip off.
Butter griddle, or a nonstick skillet, set to 350 degrees (or medium heat), and place French toast on the griddle to cook.
Cook 2 -3 minutes per side, or until the bread turns golden brown, flipping once.
Place cooked French toast on a plate, topping with butter and generous pouring of Maple syrup.
Dust lightly with powdered sugar, additional cinnamon, or brown sugar if desired.