Melt the butter over medium heat in a 12-inch skillet. Add the apples and sugar; cook 20 minutes, stirring occasionally. Stir in the apple juice; cook 1 more minute.
ASSEMBLE THE FRENCH TOAST:
Spray a 13x9-inch baking dish with nonstick spray. Arrange 1/2 of the bread slices in the dish, overlapping slightly.
In a medium bowl, whisk together the milk, salt, cinnamon and eggs. Pour 1/2 of the egg mixture over the bread. Set aside 1/4 of apple filling; cover and refrigerate to spoon on after baking. Spread the remaining apple filling over the bread in an even layer. Arrange the remaining bread slices over the apple layer. Pour the remaining egg mixture over the top bread layer. Press the bread down with a spatula so it absorbs the maximum amount of egg mixture. Dot the bread with butter and sprinkle with sugar. Cover and refrigerate overnight.
BAKE:
Preheat the oven to 325°F. Uncover the dish and bake 50 to 55 minutes or until a knife inserted into the center comes out clean. Reheat the remaining apple mixture in the microwave. Spoon over the top to serve.