1. Preheat the oven to 220°C. Line a baking sheet with parchment paper.
2. In a bowl, stir together blueberries, sugar, cornstarch, vanilla, salt and lemon zest and juice.
3. Cut the pie crusts into 6 circles with a 4 1/2-inch round cutter. Lift the circles onto the prepared baking sheet. Place about 1/4 cup of the blueberry mixture into the center of each circle. Gently fold over the edges to cover approximately 1 inch of the filling.
4. Brush the egg wash around the edge of each pastry. Sprinkle the crusts with sugar and bake until the crusts are golden and the filling is bubbly, 15 to 20 minutes.