Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.

In a medium mixing bowl, combine the softened cream cheese, granulated sugar, lemon zest, and vanilla extract. Whisk until the mixture is smooth and creamy.

Unfold the thawed puff pastry sheet on a clean surface and cut it into 8 equal rectangles.

Place the pastry rectangles onto the prepared baking sheet, spacing them apart slightly.

Using a sharp knife, lightly score a border about 1/2 inch from the edge of each rectangle. Be careful not to cut all the way through the dough.

Spoon a dollop of the cream cheese mixture into the center of each rectangle and spread it gently, staying inside the scored border.

Top the cream cheese layer with fresh blueberries, pressing them down slightly.

In a small bowl, whisk the egg with 1 tablespoon of water to create an egg wash. Brush the edges of the pastry with the mixture.

Bake for 15 to 20 minutes, or until the pastry is puffed high and golden brown.

Remove from the oven and let cool for 5 minutes. Dust with powdered sugar before serving if desired.