Wash the apples, then slice them as thinly as possible using a mandoline (or very sharp knife — but we’d recommend a mandoline for consistency). Leave the cores in the apples, but remove any seeds as you cut.
Line baking trays with parchment paper. Lay the apples on the tray in a single layer, as close as possible without touching. Sprinkle with cinnamon.
Bake for 1 to 2 hours, until as crisp as desired (a shorter baking time yields a chewier chip; baking time also depends on the thickness of the chip). Store the apple chips in a sealed container or mason jar at room temperature for about 1 week.