Slice apples cross-wise, 1/8 inch thick. Remove seeds.
Arrange on a parchment-lined baking sheet. Sprinkle with cinnamon, to taste.
Bake for 1 1/2 hours. Flip, continue baking until crisp, about 1 hour longer.
Let cool. Store in an air-tight container for up to 1 week or in the freezer for 3 months.
Notes
The cooking time will depend on the thickness of your apple slices. If they aren't crispy at the end of the recommended cooking time, allow them to continue to cook, checking crispiness every 20 minutes.