1. Preheat the oven to 375°F.
2. Remove the core from the apples using a corer. Squeeze lemon juice into the core of the apples.
3. Cut the puff pastry into squares and prick the pastry with a fork.
4. Place the apples on the pastry squares. Fill the center of the apples with brown sugar.
5. Fold the pastry over the apples, sealing the edges with a little water.
6. Brush the pastry with the beaten egg.
7. Bake for 20 minutes. Remove from the oven, let cool for a few minutes. Serve warm.