Preheat your oven to 200°F (93°C) and line a baking sheet with parchment paper.
Wash the apples thoroughly and pat them dry with a clean towel.
Using a mandoline slicer or a sharp knife, thinly slice the apples crosswise, about 1/8 inch thick. Remove and discard the seeds.
In a small bowl, mix together the ground cinnamon and granulated sugar, if using.
Arrange the apple slices in a single layer on the prepared baking sheet, making sure they don't overlap.
Sprinkle the cinnamon mixture evenly over the apple slices.
Bake the apple slices in the preheated oven for 1.5 to 2 hours, flipping them halfway through, until they are crisp and golden brown.
Once the apple chips are done, remove them from the oven and let them cool completely on the baking sheet.
Once cooled, store the apple chips in an airtight container for up to one week.