Prepare Puff Pastry: Take your puff pastry from the freezer and allow it to thaw either on the countertop for about 30 minutes or in the microwave for 10-15 seconds at a time until softened. Preheat your oven to 375°F while you wait. Once thawed, roll it out on a lightly floured surface to ensure it's nice and pliable for easy handling.

Make Filling: In a mixing bowl, beat the cream cheese and granulated sugar using a hand mixer or whisk until the mixture is smooth and creamy, about 2-3 minutes. Then, incorporate the egg yolk, lemon juice, and vanilla extract, blending well until fully combined.

Assemble Pastries: Roll out your puff pastry and cut it into 6 equal rectangles, about 3x5 inches each. Place these on a parchment-lined baking sheet, ensuring there's space between them. Score a rectangle in the center of each pastry that’s about 1 inch smaller than the outer edges without cutting all the way through. Spoon the cream cheese filling into the center of each rectangle, adding your choice of fruit or jam on top if desired.

Egg Wash: Brush the outer edges of each rectangle with an egg wash made by whisking 1 egg with a splash of water. After applying the wash, sprinkle a light layer of coarse sugar over the top.

Bake: Slide your baking sheet into the preheated oven and bake for 15-20 minutes, or until the pastries have puffed up and turned a golden brown.

Glaze (Optional): Mix powdered sugar with milk in a small bowl until smooth to create a glaze. Drizzle this over the top of the cooled pastries.