Preheat oven to 250 degrees. In a small bowl, combine the sugar and cinnamon. Using a serrated knife or mandoline, thinly slice apples crosswise, discarding the seeds and both ends. Arrange in a single layer on parchment-paper-lined baking sheets; sprinkle with the cinnamon sugar.
Bake the apple slices, turning every half hour, until dry, 1 1/2-2 hours. Remove and transfer to racks to cool. Store in an airtight container.