Slice apples thinly using a mandolin or a knife.
Place sliced apples on parchment lined cookie sheets.
Sprinkle cinnamon on the slices (you can do front and back but not too much or they will be bitter).
Cook at 225 degrees for 1 hour to 1 and a half hours (depending on how thin the apple slices are) - turning once midway.
Take them out and let them cool and enjoy!