Heat the oven to 160C/ 140C fan/ gas mark 3. Core the apple and slice through the equator into very thin slices 1 - 2mm thick. Dust with cinnamon and lay flat on a baking sheet lined with parchment paper.
Cook for 45 mins – 1 hour, turning halfway through and removing any crisps that have turned brown. Continue cooking until the apples have dried out and are light golden. Cool, store in an airtight container and enjoy as a snack.