Prepare the Strawberry Filling: In a medium bowl, combine sliced strawberries, cornstarch, and sugar. Toss until evenly coated. Set aside to release juices.

Make the Cream Cheese Filling: In another bowl, whisk together cream cheese, powdered sugar, and vanilla extract until smooth and creamy.

Assemble the Pastries: Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper. Roll out the puff pastry sheets and cut each sheet into 4 equal squares. Place a dollop of cream cheese filling in the center of each square, spreading slightly. Top with a spoonful of the strawberry filling. Fold two opposite corners of the pastry towards the center, overlapping slightly, and press lightly to seal.

Bake: Transfer the pastries to the prepared baking sheet. Brush each pastry with the egg wash and sprinkle with sugar if desired. Bake for 18-20 minutes or until golden brown and puffed.

Add Toppings: For a glossy finish, brush the pastries with warm strawberry jam immediately after baking. Mix powdered sugar, vanilla extract, and milk to create a smooth icing. Drizzle over the cooled pastries for a sweet touch.