Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
In a medium bowl, beat together the softened cream cheese, granulated sugar, and vanilla extract until smooth and creamy with no lumps remaining.
Gently fold the blueberries into the cream cheese mixture, being careful not to crush them.
Unfold the thawed puff pastry sheet on a lightly floured surface and roll it gently into a 12-inch square. Cut into 4 equal squares using a sharp knife or pizza cutter.
Place 2 tablespoons of the cream cheese-blueberry filling in the center of each pastry square. Fold one corner diagonally over to the opposite corner to form a triangle, then press the edges firmly with a fork to seal.
Transfer the croissants to your prepared baking sheet, spacing them 2 inches apart. Brush the tops generously with the egg wash.
Bake for 18-22 minutes until the pastry is deeply golden brown and puffed with visible flaky layers.
Let the croissants cool on the baking sheet for 5 minutes, then transfer to a wire rack. Dust with powdered sugar just before serving while still warm.
