Preheat the oven to 225°F (110°C).
Wash and dry the apples.
Slice the apples thinly, about ⅛ inch. You can use a mandoline or a sharp knife. Keep the peels on.
Remove any seeds from the slices.
Line two baking sheets with parchment paper.
Lay the apple slices on the sheets in a single layer. Don’t overlap them.
Lightly sprinkle cinnamon over the slices. Add a tiny bit of salt if you like.
Bake for 1.5 to 2 hours, flipping the slices halfway through.
Check for crispness. The chips should feel dry and firm.
Turn off the oven and let the slices sit inside for 10–15 minutes for extra crunch.
Cool completely on the counter.
Store in an airtight jar for up to a week.