Heat oven to 200C/400°F.
Line a baking tray with parchment paper.
In a saucepan, add the sugar, apple and lemon juice. Cover with a lid and cook over a medium/low heat for 5-10 minutes until the fruits are softened. Set aside to cool slightly.
Sprinkle a work surface lightly with flour. Roll out the puff pastry and cut into a rectangle approximately 30 X 20cm.
Brush the pastry with egg wash.
Then spoon the apple mixture on the pastry. Fold each in half to enclose the pastry. Using a fork or your fingers, press the edges together to seal.
Transfer onto the baking tray, brush with egg wash. Use sharp knife to cut a few slits ( vents to allow the pastry to cook). Sprinkle some pearl sugar over.
Bake for 25 to 35 minutes until cooked through.
Remove from the oven and let cool for 15 minutes on a wired rack if possible.
Serve within a day for best flavour!