Prepare the Cream Cheese Filling: In a mixing bowl, combine softened cream cheese, granulated sugar, and vanilla extract. Mix until smooth and creamy.

Prepare the Puff Pastry: Preheat your oven to 400°F (200°C). Lightly dust a clean surface with flour and unfold the puff pastry sheet. Roll it out slightly to remove the creases. Transfer the puff pastry onto a baking sheet lined with parchment paper.

Assemble the Danish: Spread the cream cheese mixture evenly over the center of the puff pastry, leaving a small border around the edges. Sprinkle the blueberries evenly over the cream cheese layer. If using, sprinkle the lemon zest over the blueberries for added flavor.

Shape the Danish: Fold the edges of the puff pastry over the filling, creating a border. You can also cut diagonal strips along the sides of the pastry and fold them over the filling in a crisscross pattern for a classic Danish look.

Egg Wash: In a small bowl, beat the egg with water to create an egg wash. Brush the edges and any exposed pastry with the egg wash for a golden finish.

Bake: Bake in the preheated oven for 20-25 minutes, or until the pastry is golden brown and puffed.

Cooling and Garnishing: Allow the Danish to cool slightly on a wire rack. Dust with powdered sugar before serving.