Heat the oven to 325°F. Line a baking sheet with a nonstick silicone baking mat. Thinly slice the apples on the mandolin. Sprinkle with sugar. Bake for 10 minutes. Flip each slice and dust with more sugar. Bake for an additional 10 minutes. Remove from the oven to crisp. Depending on humidity, may store in an airtight container for 2 days.