Preheat the Oven: Set to 200°C (400°F) and line a baking sheet with parchment paper.
Prepare the Apples: In a bowl, toss the sliced apples with cinnamon.
Roll Out the Pastry: Lightly flour your surface and roll out the puff pastry sheet.
Assemble the Pastry: Arrange the apple slices in the center of the pastry, leaving space around the edges.
Seal and Brush: Fold or shape the pastry as desired, then brush with the beaten egg for a golden finish.
Bake Until Golden: Place in the oven and bake for 18-22 minutes, or until puffed and golden brown.
Cool & Serve: Let cool slightly, dust with icing sugar, and enjoy warm!