Preheat oven to 225ยบ F. Line two rimmed baking sheets with parchment paper. Arrange apple slices on sheet pans in a single layer. If using cinnamon and sugar, combine together in a small bowl and sprinkle over top apple slices. Place sheet pans in preheated oven and bake 45 minutes, flip apple slices over and bake another 30 minutes or until crisp. Store in an airtight container for up to a week.
Notes
Variations: Instead of cinnamon and sugar, sprinkle apples with apple pie spice.