Preheat your oven to 375 degrees F and line a baking sheet with parchment paper. Set aside.
Unwrap the two pie crusts (if using store-bought) and lightly go over each one with a rolling pin to make them a touch more thin and smooth.
Using a sharp knife, trim the edges of each pie crust to create two even rectangles.
Transfer one pie crust to the prepared sheet pan and evenly spread on the jam, making sure to leave a 1 inch boarder around the edge.
In a small bowl, whisk the egg with 1 tbsp water to create an egg wash. Using a pastry brush, brush the egg wash around the 1 inch boarder of exposed pie crust.
Lay the second pie crust directly on top of the first and use your index finger to lightly press and seal the edges of the pie crust together.
Using the prongs of a fork, crimp the edges of the pastry by pressing straight down to make indentations along the boarder.
Dock the top of the poptart by poking a few holes on the surface with the prongs of your fork. This will let air escape while it bakes.
Brush the remaining egg wash all over the surface of the poptart, then make for 20 minutes.
While the poptart cools, combine the icing ingredients in a medium bowl. If it seems too thin, add more powdered sugar. If it seems too thick, add a little more milk.
Spread the glaze evenly overtop of the cooled poptart. Optionally decorate with sprinkles!