Prepare a baking sheet with parchment paper.

Preheat oven to 400 degrees F.

In a small bowl, combine the egg and water with a fork and set aside.

In a small mixing bowl, add the blackberries, sugar, flour, and vanilla and mix gently. set aside.

On a floured work surface, unfold and place puff pastry.

Using a floured rolling pin, roll out puff pastry into a rectangle, about 12”x14”.

Move pastry onto prepared baking sheet.

In a small microwaveable dish, heat blackberry preserves for about 10 seconds.

Spoon and spread preserves the long way down the middle of the pastry.

Spoon blackberry mixture over the preserves, keeping in the center the long way.

Along each long side, cut 3 inch long slits every inch .

Starting at the top, begin folding the slits in, overlapping slightly downward, alternating sides, over the blackberry filling.

Brush egg wash over the top.

Sprinkle remaining sugar on top.

Bake for 21-23 minutes, or until golden brown.

Allow pastry to cool for 10-15 minutes on the baking sheet before serving.