Preheat your oven to 200F.
Line two baking sheets with parchment paper. I use one large baking sheet and one medium one because it fits in my oven and allows me to bake all my slices in one session.
Remove the center of the apples using an apple corer or sharp knife.
Slice the apples into rings that are between 1/8 and 1/16 inch thick. I love using this super simple mandoline slicer to make the process quick and easy while also getting even slices, but you can use a sharp knife to cut them, too.
Place the apple slices in a single layer on your lined baking sheets.
Sprinkle the cinnamon over the apples. Tip: If you have a mesh strainer, place the cinnamon in the basin and then position it over the apple slices. Tap it gently to create an even coating of cinnamon on the chips. I use the smallest strainer I have because it's the easiest to work with.
Place the apple slices in the oven and bake for 1 hour, then flip and set the timer for 1 more hour. When the time is up, remove one slice and let it cool for 5 minutes before testing for crispiness. Chances are it will still be pretty soft, but it's good to check early so that they don't burn. If they're still soft, continue baking for 30 more minutes and then check again.
If you're happy with the level of crispiness after baking 30 more minutes, turn off the oven and leave the apple chips inside to continue to continue to crisp up for the next hour or so. Dried fruit can absorb moisture from the air so you want them to be a little drier than your preferred "target crispiness level" when you take them out.
If you're not happy with the level of crispiness after baking those additional 30 minutes, continue baking while checking on them every 15 minutes or so.
Store in an airtight container for up to one week.