Cut bread into 1 1/2 inch thick slices and place in a lightly greased 9x13 inch baking pan. In a large bowl, beat eggs with 1 1/2 cup skim milk, 1/3 cup white sugar, and 1 tablespoon vanilla. Pour egg mixture over bread slices.
Arrange apple slices on top of bread. Sprinkle cinnamon, nutmeg, and 2 tablespoons white sugar over apples. Cover, and refrigerate overnight.
In the morning: Preheat oven to 350 degrees F (175 degrees C).
Bake toast in preheated oven until golden brown, about 1 hour. Meanwhile, combine 1/2 cup white sugar, flour, and margarine. Stir in brown sugar, 1/2 cup skim milk, and 2 teaspoons vanilla in a small saucepan. Cook until thick. Serve French toast hot with warm sauce.
