Preheat oven to 200°F (93ºC).

Line two large baking sheets with parchment paper or a silicone baking mat.

Sift powdered sugar into a bowl. Add cinnamon to the powdered sugar and gently whisk to combine.

Thinly slice the apples using a mandoline, to 1/16-inch. Remove the seeds from the individual slices.

Spread the apple slices onto the lined baking sheets making one single layer. About 15 slices should fit on a half sheet pan.

Transfer the cinnamon and sugar mixture into a sifter or strainer. Gently sprinkle each apple slice with a thin coating of the cinnamon sugar mixture.

Turn the apple slices over and sprinkle with the remaining cinnamon-sugar.

Bake for 1 hour, then flip and bake until crisp, an additional 1 hour.

To test the doneness, remove the apples from the oven and allow to rest at room temperature for 5 minutes. If the apples are not crunchy, continue baking in 15-minute increments.

Remove the apples from the baking sheets and allow to cool completely before storing in an airtight container.