Slice bread into 1-1/2" slices.
Spray a 9x13" glass pan with cooking spray.
Place bread in pan with sides touching, will be a snug fit.
Whisk together eggs, 1/2 c. sugar, milk and vanilla for about 30 seconds.
Pour half of mixture over bread.
Place apples on top of bread to cover.
Pour rest of egg mixture evenly over bread.
Mix 1/2 c. sugar with cinnamon and nutmeg and sprinkle evenly over apples. Dot with butter.
Cover and refrigerate overnight. In morning, preheat oven to 350°. Uncover dish and bake for one hour.
Remove from oven and allow to rest 5-10 minutes. Cut into squares and serve with warm syrup or powdered sugar.