The day before serving, prepare the apples and French toast.
In large, heavy skillet, melt butter over medium heat. Add apple slices and cook, stirring occasionally, until tender.
Add brown sugar, corn syrup, and cinnamon to apples. Cook stirring, until brown sugar dissolves.
Pour apple mixture into 13 by 9 inch baking pan and spread to even layer.
Arrange bread slices in one layer on top of apple mixture.
In medium-size bowl, with fork, beat eggs, milk, and vanilla extract until well mixed; pour over bread slices.
Cover with plastic wrap and refrigerate overnight.