Preheat your oven to 400º F and line a baking sheet with parchment or a silicone baking mat.
To a small saucepan over medium heat add the apples, lemon juice, brown sugar, cinnamon and corn starch, stir to combine and cook until tender about 6-8 minutes. Set aside to cool slightly.
Slice your sheet of puff pastry into 4 equal pieces and place on the baking sheet.
Add a scoop of the apples (make sure to reserve 1 Tbs of the liquid from the cooked apples) to the lower right section of the pastry and fold the left top corner down to meet the right one, forming a triangle. Using a fork crimp the edges of the pastry to close.
Place the baking sheet in the oven and bake for 15-17 minutes until golden brown on top, let cool on the pan.
In a small mixing bowl combine the powdered sugar, reserved cooking liquid and vanilla, stirring until smooth.
Drizzle the pastries with the icing and serve warm.
Remember to reserve 1 Tbs of the liquid from the cooked apples for the icing.
Recipe by It Bakes Me Happy at https://itbakesmehappy.com/2017/11/easy-apple-cinnamon-turnovers.html