Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper.

In a medium saucepan, combine fresh blueberries, sugar, brown sugar, lemon zest, lemon juice, and cornstarch. Cook over medium heat until thickened, about 5-7 minutes. Remove from heat to cool.

In a mixing bowl, beat cream cheese until smooth. Blend in egg yolk, sugar, vanilla extract, and a squeeze of lemon juice.

Roll out one puff pastry sheet on a floured surface, place it on the lined baking sheet, and spread the cream cheese filling evenly over it. Spoon the cooled blueberry filling on top.

Roll out a second pastry sheet over the filling and slice into diagonal strips. Roll each strip into a crescent shape.

In a bowl, whisk together an egg with a tablespoon of water to create an egg wash. Brush this over the tops of the pastries.

Bake for about 20 minutes, until puffed and golden brown. Watch closely to avoid over-browning.

Remove from the oven and let cool for a few minutes. Dust with powdered sugar before serving.