Preheat your oven to 400°F (200°C).
In a mixing bowl, combine the cream cheese, granulated sugar, milk, and vanilla extract. Blend until smooth and creamy.
Gently toss the blueberries with lemon juice and flour.
Roll out your sheet of puff pastry into a rectangle about 1/4 inch thick and cut into squares.
Place a tablespoon of the cream cheese filling in the center of each puff pastry square, add blueberries, and fold corners to seal.
Beat one egg and brush each pastry with egg wash.
Bake for about 20 minutes or until puffed and golden brown.