Preheat oven to 375°F and line a baking sheet with parchment paper. Set aside.
Roll one of the pie crusts out a bit on a countertop. Cut off the rounded edges to make a large rectangle. Cut 6 equal smaller rectangles from the dough, then repeat with the other pie crust.
2 9-inch refrigerated pie crusts
Mix the blueberry preserves with the cornstarch in a small bowl, then add 2-3 tablespoons of it to the center of one of the dough rectangles. (Don’t overfill the dough or you will get overflow once you seal the edges.)
½ cup blueberry preserves, 2 teaspoons cornstarch
Whisk the egg in a small bowl then brush it around the sides of the dough and set another piece of dough on top.
1 large egg
Press the edges of the dough down with a fork to seal the dough together, trim off any excess to create clean lines, then set the pop tart on the baking pan and brush some egg on top. Repeat this process with the remaining dough and preserves.
Gently prick one or two holes in the top of each pastry with a toothpick or the tines of a fork to prevent blowouts, then bake for 10-12 minutes or until light and golden on top.
While they are baking, make the icing. Mix the powdered sugar, blueberry preserves, milk, and vanilla together until smooth.
½ cup powdered sugar, 1 tablespoon milk, ½ teaspoon pure vanilla extract, ¼ cup blueberry preserves
Drizzle the icing on top of the pop tarts once they are cool to the touch, and let them dry for 10 minutes before serving.