Whisk together the eggs, milk, vanilla, powdered sugar, cinnamon, and nutmeg in a large bowl.

Lightly butter or spray a 9 by 13-inch pan. Arrange the bread slices in the pan. (The bread should fill the pan, only leaving spaces around he curves. If you use a baguette-sized loaf, you will need additional slices.) pour the egg mixture over the bread and turn each slice over to thoroughly coat. Cover the pan with plastic wrap and refrigerate for 1 hour, or up to 1 day.

Preheat the oven to 325°F Fahrenheit.

Place a small piece of the butter on top of each piece of bread. Bake the French toast for 25 to 30 minutes, or until light brown. (The French toast will puff up during cooking and fall as soon as it is removed from the oven.)

Serve with maple syrup, jam, or fresh berries.