Line a cookie sheet with parchment paper and place the sliced apples on top.
Sprinkle with cinnamon (to taste).
Bake for two hours. After 60 minutes, turn each slice over so they bake evenly. You should check on them after 60 minutes and every 30 minutes after that because oven cook times vary and you don’t want to burn them.
Once they look nice and crispy, remove them from the oven and allow them to cool.