Preheat your oven to 400˚F (200˚C) and line a baking sheet with parchment paper.

In a medium bowl, combine mixed berries with lemon juice, lemon zest, maple syrup, and cornstarch. Let sit for 5 minutes.

Roll out the thawed puff pastry on a floured surface to about 1/8 inch thick and cut into four rectangles (4x6 inches).

Place the pastry rectangles on the prepared baking sheet, leaving 2-inch spaces between them.

Spoon the berry mixture into the center of each pastry rectangle, leaving a ½ to 1-inch border around the edges.

Fold the edges of the pastry over the berry filling and pinch corners together. Brush the edges with the egg wash.

Bake for 20-25 minutes until golden brown and puffed up.

Once baked, let cool slightly before serving with vanilla ice cream or whipped cream.