If you want to test them for crispness, pull one apple out and let it cool for 2-3 minutes before testing.
Preheat oven to 220 degrees F. Line 2 baking sheets with parchment paper or silpat.
Wash the apples – core them if you have an apple corer and thinly slice with mandolin or sharp knife (mandolin is easiest). If you don’t have an apple corer, just thinly slice and remove seeds.
In a bowl mix the cinnamon and apples. Start with ¾ teaspoon and add more as needed. You can always skip this step if you want and sprinkle the cinnamon on top of the apples on the baking sheet, but we find this step helpful to evenly distribute the cinnamon.
Arrange apples on single layer of baking sheet. Cook for 1 hour then flip and cook for another hour. Turn off the oven and let them cool inside the oven to crisp up.