Preheat your oven to 375°F (190°C).
Roll out the puff pastry sheet on a lightly floured surface to ensure it's even.
Place the Brie wheel in the center of the pastry. Top the Brie with blackberry jam.
Fold the puff pastry up and around the Brie, sealing it well, and trimming any excess pastry if necessary.
Mix the beaten egg with water to make an egg wash, then brush the surface of the wrapped Brie with the egg wash.
Place the wrapped Brie on a baking sheet lined with parchment paper.
Bake for 20 minutes, or until the pastry is golden brown and puffed.
Remove from the oven and let it cool for a few minutes before serving.