Preheat the oven to 200 degrees Celsius/ 400 degrees Fahrenheit. Line two baking trays with baking 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.
Mix the sugar and the cinnamon in a small bowl.
Melt the butter in a small pot.
Unroll one rectangle of pastry on your working surface. Brush with half of the butter and sprinkle with half of the sugar-cinnamon mixture.
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 3 cm/ 1.18 inch 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.
Refrigerated puff pastry sheets. If the puff pastry is frozen, thaw and roll according to the packet's instructions. They should be about 25 cm/ 10 inches long. The exact size is not of vital importance; a bit more or less should be OK.