Peel and dice the apple. Place the apple pieces in a bowl and add the sugar and cinnamon. Stir well to combine.
Spread the apple-cinnamon filling over the puff pastry slices, leaving the edges free of the filling. Fold in half diagonally and press down the edges with a fork.
Beat the egg and brush the apple turnovers with it, then sprinkle with cinnamon sugar.
Bake for 15-18 minutes at 200 °C/400 ℉ (conventional).
How to store
Keep them covered outside the fridge for about 2-3 days.