Preheat your oven to 200°F (95°C). Line a baking sheet with parchment paper or lightly spray it with cooking spray.
Wash and core the apples. Using a mandoline or a sharp knife, slice the apples into thin rounds, about 1/8 inch thick.
In a small bowl, mix the ground cinnamon and sugar (if using).
Arrange the apple slices in a single layer on the prepared baking sheet. Sprinkle the cinnamon-sugar mixture evenly over the apple slices.
Bake in the preheated oven for 1.5 to 2 hours, flipping the apple slices halfway through, until they are dry and crisp.
Once done, remove the apple chips from the oven and let them cool completely on the baking sheet. They will become crispier as they cool.