Pre heat oven to 180°C/350°F/160°FF
Add the flour, sugar and butter to a food processor and process until the mixture resembles fine breadcrumbs.
Keep the motor running and drizzle in the iced water. Mix just until it becomes a smooth dough.
Lightly knead the dough, divide into 3 balls (160g each) then wrap separately in plastic and refrigerate for 30 minutes.
Roll each pastry ball, one at a time, into a rectangle measuring 15cm x 20cm. Using a knife or pastry cutter, cut that rectangle into 4 smaller rectangles, each measuring 7.5cm x 10cm. Using the 3 dough balls, you will end up with 12 rectangles.
Reserving a little of the filling for the glaze, place a small dessertspoon of the blueberry filling onto 6 of the rectangles. Keep the filling clear of the edges, to allow space for sealing the dough.
Brush the egg wash onto the edges of the filled rectangles, then cover them with the remaining 6 rectangles (you can gently stretch the dough a little, to ease it over the filling).
Use a fork to seal and crimp the edges of the pop tarts (you can re-cut the edges if you want to neaten them up).
Egg wash the top of each Pop Tart then cut small holes into the top, to allow steam to escape during baking.
Bake for 20 minutes, until golden, then set on a cake rack to cool completely. You may get little cracks in the pastry, but they will be covered with the blueberry glaze.