**Preheat the Oven:** Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper.

**Prepare the Cream Cheese Filling:** In a bowl, mix the softened cream cheese, granulated sugar, and vanilla extract until smooth and creamy. Set aside.

**Prepare the Blueberries:** In a separate bowl, toss the blueberries with cornstarch and 2 tablespoons of sugar. Set aside.

**Roll Out the Puff Pastry:** On a lightly floured surface, unfold the puff pastry sheet. Cut it into rectangles or squares, depending on your desired shape.

**Assemble the Pastries:** Place a spoonful of cream cheese mixture in the center of each pastry piece, then top with a small spoonful of the blueberry mixture. Be careful not to overfill.

**Fold and Seal:** Fold the pastry over the filling to create a pocket or leave the filling exposed for an open-faced look. Press the edges together with a fork to seal, if necessary.

**Egg Wash:** In a small bowl, whisk together the egg and water. Brush the egg wash over the pastry for a golden finish.

**Bake:** Transfer the pastries to the prepared baking sheet and bake for 15–20 minutes, or until golden brown and puffed.

**Cool and Serve:** Let the pastries cool slightly. Dust with powdered sugar, if desired, before serving.