Wash and slice apple(s) very thinly (you want to aim for about 1/8” slices). Prior to slicing you can core the apples if you prefer…I usually just slice and then will discard the seeds before baking.
Lay the apple slices on a parchment paper-lined large baking sheet so none of them are touching or on top of each other. One full apple is usually about 1 large baking sheet.
Sprinkle the apple slices with cinnamon. I sprinkle about 1/2 tsp cinnamon for each large baking sheet. If you’re baking more than just one, just add about 1/2 tsp per each baking sheet (or as much or as little as you want!).
Bake for 1.5 – 2 hours, depending on how thin they are.
Take them out of the oven when they get crispy, let cool, and enjoy.