Preheat oven to 200 degrees C. Line a baking tray with parchment paper or foil.
In a large frypan melt the butter over medium heat; reserve 1 tablespoon in a small bowl. Add the apples, sugar and cinnamon. Increase heat to medium-high then cook, tossing occasionally, until apples are tender and liquid has evaporated; about 15 minutes. Let the apples cool completely.
Place the puff pastry on the baking tray, mound filling in a strip across the centre, leaving a 3cm border on both long sides. Fold top part, then bottom part of dough over filling. Turn pastry over, seam side down.
Brush pastry with reserved melted butter. Sprinkle with additional sugar. Using a small knife cut steam vents in centre of pastry. Bake until golden brown, 35 to 40 minutes. Let rest 10 minutes before serving.