Whisk egg and milk until smooth, set the egg wash aside for later.
1 large egg, 1 tablespoon milk
On a lightly floured surface, roll out both pieces of crust to form two squares, ¼ inch thick. Trim the edges even.
Use a knife to score one of the rolled out pieces into 6 rectangles (or more if you prefer smaller pop tarts). Fill the middle of each with cooled blueberry filling. Reserve the bowl from the blueberry filling for the glaze. Brush in between the fillings to help the crusts seal.
Place the second square on top and use your fingers to press down in between each pop tart to help seal the edges. Use a pizza cutter or sharp knife, cut into individual pop tarts.
Use a fork to firmly press down on all the edges to seal. Poke the tops to allow steam to escape. Transfer to a parchment lined baking sheet leaving 1-2 inches between each pop tart.
Place pop tarts into the freezer for 10 minutes. While they’re chilling, Preheat the oven to 375°F (190°C).
Brush tops of the chilled pop tarts with egg wash and sprinkle liberally with coarse sugar. Bake for 20 minutes, until they are golden brown. Let the pop tarts cool on the baking sheet for 10 minutes.
2 tablespoons coarse sugar