Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper.
Let the puff pastry sheet thaw for 10–15 minutes.
Roll it out on a lightly floured surface until about ⅛-inch thick.
Cut into 6 equal rectangles or squares.
Thinly slice the apples and remove the core and seeds.
Arrange the apple slices on each piece of pastry, fanning them or lining them up in rows. Leave a ½-inch border around the edges.
In a small bowl, mix the sugar and cinnamon.
Sprinkle evenly over the apple slices.
Brush apple slices lightly with melted butter for added flavor and browning.
Beat the egg and brush the exposed edges of the puff pastry.
This helps the edges puff up and turn golden during baking.
Place pastries on the prepared baking sheet.
Bake for 15–18 minutes, or until the pastry is puffed and golden and the apples are tender.
Optional: Drizzle warm pastries with honey or caramel, or dust with powdered sugar.
Let cool for 5–10 minutes before serving.