Thinly slice the apple. Line a large baking pan with parchment paper. Place the sliced apples in a single layer on the baking pan.
Sprinkle some cinnamon on top of each apple slice.
Bake in the oven for 1 to 1-1/2 hours. After 1 hour, turn the apple slices over and continue to bake so that each side bakes equally. After the hour, check every 15min and remove from the oven when they are crispy.
Remove the apple slices before they start to turn brown and be sure not to burn them. Enjoy!
How To Core Apples - The best way to core an apple is with an apple corer shown above. It is easy and works perfectly. So I highly recommend getting your hands on a cheap apple corer.