In a large bowl, combine flour and sugar. Add cold butter and use a pastry cutter to incorporate until the mixture resembles coarse crumbs.
Gradually add cold water and mix until a dough forms. Wrap in plastic and refrigerate for 30 minutes.
Preheat oven to 375°F (190°C). Roll out the dough on a floured surface to about 1/8 inch thickness.
Cut into rectangles and place a small spoonful of blueberry preserves on one half of each rectangle. Brush the edges with egg wash, fold over, and press the edges to seal.
Place the prepared pastries on a baking sheet lined with parchment paper. Brush the tops with egg wash.
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