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 tbsp vanilla.
Pour egg mixture over bread slices.
Arrange apple slices on top of bread.
Sprinkle cinnamon, nutmeg, and 2 tbsp white sugar over apples.
Cover, and refrigerate overnight.
In the morning: Preheat oven to 350 degrees.
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 tbs vanilla in a small saucepan.
Cook until thick.
Serve French toast hot with warm sauce.
Ready in 15 hours.