Giant Blueberry Poptart

In a large mixing bowl, cut the cubed butter into the all purpose flour using a bench scraper, fork, or your hands until the butter is incorporated. Alternatively, you could do this in a food processor. Pour in the cold water and mix with your hands until a dough forms. Cut the dough in half, and roll out each piece until it is 1/4 inch thick (about 9 x 13). Using a knife or bench scraper, clean up the edges. Transfer one of the slabs of dough to a parchment paper lined baking sheet. Spread 1 cup of blueberry jam (you can make your own like I did or use store bought!) evenly over the dough, leaving about 1/2 inch around the edges. Carefully place the other slab of dough on top and seal the edges using a fork. Poke a couple of holes in the dough using the fork. Place in the freezer for 30 minutes while your oven preheats to 350F. Whisk together the egg with 1 tbsp of water and brush the poptart with this egg wash. Transfer to the oven and bake for 30-35 minutes, or until the golden brown. Let the poptart cool for 15 minutes. Whisk together the powdered sugar, remaining 1 tbsp of blueberry jam, heavy cream, and vanilla until smooth and top the poptart with it. Slice and enjoy!