Preheat the oven to 400°F/ 200°C. Line two baking sheets with parchment paper.
Peel and chop the apples into very small cubes. Immediately mix the cubes with 2 tablespoons lemon juice and just a little bit of the grated lemon zest.1 large apple + a pinch of zest from 1 organic lemon + 2 tablespoons fresh lemon juice
Mix the sugar and the cinnamon in a small bowl.6 tablespoons granulated sugar + 1 teaspoon cinnamon
Melt the butter in a small pot.2 tablespoons unsalted butter
Unroll one rectangle of pastry on your working surface. Brush with half of the butter and sprinkle with half of the sugar-cinnamon mixture.2 puff pastry sheets
Spread the apple cubes all over the pastry. Cover with the second puff pastry rectangle. Brush this pastry sheet with the remaining butter and sprinkle with the remaining sugar-cinnamon mixture.
Roll up the pastry starting from the long side and make sure that the seam faces down. Using a sharp knife, cut the roll into 1.2 inch/ 2 cm wide pieces.
Bake: Place them on the prepared baking sheets leaving some space between them, and bake for about 20-25 minutes or until golden brown and crispy.
Let cool on the baking sheets and serve as fresh as possible.
Notes
Refrigerated puff pastry sheets. If the puff pastry is frozen, thaw and roll according to the packet's instructions. They should be about 10 inches/ 25 cm long. The exact size is not vitally important; a bit more or less should be OK.