Preheat your oven to 400°F (200°C). Prepare a baking sheet by lining it with parchment paper to prevent sticking.
On a lightly floured surface, carefully roll out the thawed puff pastry sheet to smooth out any creases and ensure even thickness. Once rolled, cut the sheet into 4 equal squares.
In a mixing bowl, use an electric mixer or a whisk to combine the softened cream cheese, powdered sugar, granulated sugar, vanilla extract, egg yolk, and fresh lemon juice. Beat until the mixture is smooth, creamy, and well-blended.
Spoon a generous amount of the creamy cheese mixture into the center of each puff pastry square, ensuring not to overfill to allow for proper sealing.
Fold the corners of each square toward the center, enveloping the cheese filling and creating a small bundle. Make sure to pinch the corners securely to seal them and prevent leakage while baking.
Using a pastry brush, gently apply the beaten egg on top of each Danish to achieve a beautiful golden-brown finish once baked.
Carefully transfer the prepared Danish to the lined baking sheet. Bake in the preheated oven for 15-18 minutes, or until the pastry is puffed up and turns a lovely golden brown.
Once baked, remove from the oven and allow the Danish to cool for a few minutes on the baking sheet before transferring to a wire rack. Just before serving, feel free to top with fresh berries for a pop of color and an added burst of flavor.