Prepare the Blueberry Filling: In a saucepan over medium heat, combine blueberries, lemon juice, cornstarch, and granulated sugar. Cook for about 5-7 minutes until the blueberries soften and the mixture thickens slightly. Remove from heat and let it cool.
Make the Cream Cheese Filling: In a mixing bowl, beat the softened cream cheese, powdered sugar, vanilla extract, and lemon zest until smooth and creamy. Set aside.
Preheat the Oven: Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
Roll Out the Puff Pastry: Unroll the thawed puff pastry sheet on a lightly floured surface. Cut the pastry into squares (approximately 4x4 inches).
Assemble the Danishes: Place 1 tablespoon of the cream cheese mixture in the center of each pastry square. Top with 1 tablespoon of the blueberry filling over the cream cheese.
Fold and Seal: Fold the corners of the puff pastry over the filling to create a diamond shape, pinching the corners to seal. Brush the tops lightly with the beaten egg wash.
Bake: Sprinkle a little granulated sugar over the tops for added sweetness and crunch. Bake in the preheated oven for 15-20 minutes or until the pastries are golden brown and flaky.
Cool and Serve: Allow the danishes to cool for a few minutes on a wire rack before serving.