I sprinkled all of my apples pretty heavily with cinnamon. Next time I'll do a mix of cinnamon coated and plain as I think they would be equally delicious without spice.
Arrange apple slices in a thin, fairly even layer over parchment. You'll have some overlap.
Sprinkle generously with cinnamon. (Leave some plain if you like - see headnote)
Bake 8-9 hours, rotating the baking sheets among the 3 levels a couple of times.
Turn off the oven and open the door a crack; allow oven and apples to cool.
Allow to cool completely, then store in an airtight container for a week at room temperature, 1 month in the refrigerator, or much longer in the freezer.