01 - Preheat the oven to 400°F (200°C) and line a baking tray with parchment paper.
02 - In a small bowl, mix cream cheese, granulated sugar, vanilla extract, and lemon zest until smooth and creamy. Set aside.
03 - In a separate bowl, toss diced strawberries with granulated sugar, lemon juice, and cornstarch. Set aside.
04 - Roll out the puff pastry sheet and cut into 8 even squares. Score a 1/2-inch border around each square, taking care not to cut all the way through.
05 - Place 1 tablespoon of the cream cheese filling in the center of each square and gently spread within the border. Top with 1 tablespoon of the strawberry mixture.
06 - Brush the pastry borders with egg wash made from the beaten egg and milk.
07 - Transfer to the prepared baking tray and bake for 18 to 22 minutes until puffed and golden brown.
08 - Allow pastries to cool slightly on a wire rack before glazing.
09 - For the optional glaze, whisk powdered sugar, milk, and vanilla extract in a bowl until smooth. Drizzle over cooled pastries if desired.