Directions

1. Adjust the oven rack to the lower third position and preheat the oven to 400°F. Line two large baking sheets with parchment paper or a silpat mat and set aside
2. Make the filling first. Stir the blueberries, granulated sugar, cornstarch, and lemon juice and zest together in a large bowl. Set filling aside as the oven preheats.
3. Prepare the pastry by carefully unrolling the sheets onto a lightly floured surface. Cut each into 4 equal squares by cutting down the center both ways. Spoon 2-3 tablespoons of blueberry mixture onto the center of each square. Fold each over by connecting two pointed corners into a triangle shape. Crimp all of the edges together with a fork to seal the filling inside. Some blueberry juices may leak out.
4. Lightly brush the top of each turnover with the beaten egg. Cut 2 or 3 small steam vents in the tops of each pastry. Bake for 20 minutes until golden brown. Rotate the pan halfway through bake time if necessary to avoid uneven browning.