1 Turn oven to lowest setting. 

2 Fill a bowl with cold water and sprinkle over the lemon juice. Using a mandoline or very sharp knife, slice apples directly into the bowl of water.

3 Line a baking sheet with parchment paper and place the apple slices on the sheet after shaking off the excess liquid off it.

4 Sprinkle with cinnamon, if using and sugar. Place in oven for at least 2 hours, until the apple slices are crisp and dry.