In a food processor or by hand, stir together the flour and salt. Sprinkle very cold butter over the top and pulse for a few seconds or cut the butter with the pastry cutter/fingertips until it is about the size of split peas.

Sprinkle half of the ice water over the flour mixture and mix gently to dampen flour. Add the remaining water in two stages and continue to pulse or stir until a dough forms. When enough water has been added to allow dough to hold together, gather it into a ball and transfer to lightly floured surface. Press dough into a flat disk, then place in large zipper bag. Refrigerate dough for at least an hour or overnight.

Cut dough in half. Keep the second half wrapped in plastic wrap and in the fridge. Roll out one half of the dough onto a lightly floured surface to a 13 by 11 inch rectangle (about ¼ inch thick). Trim dough so sides are even and straight, to a 12 by 10 inch rectangle.

Cut the dough into eight 5 by 3 inch rectangles. Arrange 4 rectangles onto a parchment lined baking sheet.

For each rectangle, place one tablespoon (to 2 tablespoons max) of filling in the center. Spread out but leave a ½ inch border. Place another rectangle on top and use a fork to crimp the edges to prevent the filling from leaking out in the oven. Poke the top of each poptart with a few holes with the tines of a fork to allow steam to escape as they bake.

After they are all prepared, refrigerate to firm up again for another 30 minutes. Repeat with the remaining dough disk.

When ready, preheat the oven to 375℉ (190℃). Make egg wash and brush each poptart with a little egg wash. Place the prepared cookie sheet in the pre-heated oven. Bake for 20-25 minutes until golden brown. Place on a cooling rack before applying glaze.

Combine all three glaze ingredients and stir to combine. You may find you need to add either more powdered sugar or milk to achieve the desired consistency. Sprinkle on sprinkles.