Coat a 13x9x2-inch baking dish (3-quart rectangular) with some nonstick cooking spray and set aside.
Cut the bread into 1-1/2-inch-thick slices (about 8 slices). Arrange slices in a single layer in the baking dish.
In a large bowl, beat together eggs, milk, first 1/2 cup sugar, and vanilla. Pour half of the mixture over bread slices. Arrange apple slices over bread. Pour remaining mixture evenly over apples.
Stir together remaining 1/2 cup sugar, the cinnamon, and nutmeg. Sprinkle the mixture evenly over the apples. Dot with butter. Cover bread mixture with foil and refrigerate overnight.
Bake, covered, in a 350 degree oven for 20 minutes. Remove foil. Bake 40 minutes more or until a knife inserted in the center of the bread comes out clean. The toast should be nicely puffed. Remove the French toast from oven and let it rest for 5 to 10 minutes.
Cut into squares and serve with syrup. Makes 12 servings.