Preheat oven to 400°.
Slice apples crosswise into 1/2-inch slices. Set aside 8 largest slices; reserve remaining apple for another use.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour, granulated sugar, salt, and nutmeg in a medium bowl. Stir in cider and egg whites (batter will be thick).
Heat a large nonstick skillet coated with cooking spray over medium-high heat. Dip 4 apple slices in batter; place in pan. Cook 2 minutes on each side or until lightly browned. Arrange apple slices on a baking sheet coated with cooking spray; lightly coat apple slices with cooking spray. Repeat procedure with remaining apple slices.
Bake apple slices at 400° for 10 minutes or until edges are crisp. Drizzle each of 4 plates with 1 tablespoon caramel sauce; top with 2 apple slices. Sprinkle with powdered sugar, if desired. Serve immediately.