Preheat oven to 300 degrees F.

Preferably using a mandoline, slice apple chips very thinly, probably on the finest setting, about 1/16th of an inch. Place on a sprayed rack (preferred) or a parchment-lined sheet tray. Sprinkle with cinnamon sugar if desired.

Place in oven, immediately turn down to 250 degrees and bake for about one hour, turning the apple slices over and rotating trays top to bottom & front to rear halfway through the baking time. If using cinnamon-sugar, sprinkle again after the apple slices are turned over.

After the hour is up and/or the apples are lightly browned and crisping, turn the oven off, crack the door and let cool in the oven. Apples will be crispier after they cool.

Notes:

• Timing will vary depending on your oven and the thickness of the apples. Watch closely, especially the first time.
• Thicker apple slices may take up to two hours to bake, turning halfway through.
• Slices keep indefinitely tightly sealed, but will lose their crispiness. Best the same day.

UPDATE: Just to repeat the directions for emphasis. You HAVE to “slice apples very thinly, preferably on the finest setting, about 1/16th of an inch”  and bake as directed on “a sprayed rack (preferred) or a parchment-lined sheet tray” and “Timing will vary depending on your oven and the thickness of the apples.” They will not work right baked right on a sheet tray w/o parchment.

Do watch carefully the first time.