Preheat the oven to 200°F to 225°F
Line baking sheets with parchment paper
Wash and dry apples
Core the apples if desired
Slice apples very thinly and evenly
Remove any seeds
Arrange slices in a single layer on the baking sheets
Sprinkle with cinnamon if desired
Bake for 1.5 to 3 hours, flipping halfway through
Check until the slices are dry and crisp
Remove from the oven and let cool completely
Store in an airtight container