Pre-heat oven to 400°F.
Unfold the pastry sheet on a lightly floured surface and roll to a roughly 10×15 rectangle. Trim off the uneven edges. Place on a parchment lined baking sheet and refrigerate for 10-15 minutes.
In a small bowl, combine cream cheese, honey, vanilla, and salt and mix until smooth. Set aside.
Beat the egg in a small bowl with a splash of water. Remove puff pastry from the refrigerator and prick the center of the pastry with a fork. Brush the edges with the egg wash and transfer to oven and bake for 8 minutes.
Remove puff pastry from the oven and gently push down. Spread the cream cheese mixture on the crust. Place the blackberries on top and return to the oven and bake an additional 10 minutes until pastry is golden and puffy. Sprinkle with flaky salt (if using) and serve warm. Enjoy!
