Preheat the oven to 225 degrees F (107 degrees C). Slice apples into very thin rings. I leave the core in because I think it makes a prettier apple chip, but you can remove it if you like.
Place the baking sheet in the oven. Baking time will depend on the thickness and water content of your apple slices. They should be done in 1 ½ to 2 hours. You’ll know they’re finished when they’re crisp.