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

In a medium bowl, beat the softened cream cheese, granulated sugar, lemon zest, and vanilla extract together with a spoon or hand mixer until completely smooth and creamy.

Unroll the thawed puff pastry sheet onto a lightly floured surface and cut it into 8 equal rectangles, then place them onto the prepared baking sheet.

Use a sharp knife to gently score a border about half an inch from the edge of each pastry rectangle, being careful not to cut all the way through.

Prick the center area inside the border a few times with a fork to prevent it from rising too high.

Spoon about one tablespoon of the sweetened cream cheese mixture into the center of each pastry, spreading it evenly within the scored borders.

Top the cream cheese layer with 6 to 8 fresh blueberries, pressing them down gently so they stay in place.

Brush the outer pastry borders with the beaten egg and sprinkle the edges lightly with the coarse sparkling sugar.

Bake for 18 to 20 minutes until the pastry is puffed and beautifully golden brown on the edges.

While the pastries cool slightly, whisk the powdered sugar and lemon juice together in a small bowl until smooth, then drizzle over the warm pastries right before serving.