take the frozen dough out of the freezer, and roughly divide it into five balls, approximately the same size each. place all but one dough ball back in the freezer so they remain cold and firm until you're ready to use them.
take a piece of parchment paper and lay it atop a flat surface (counter or cutting board will do). divide your one of ball into two roughly the same size. place one of the dough balls on top of the paper, before adding a second piece of parchment paper to cover the dough. you'll be rolling out the dough between the two layers in order to facilitate the rolling, as the dough is very sticky!
roll out the dough so it's roughly 7 cm x 10 cm - it may be a bit larger or smaller give or take. you can make a rough rectangular shape at first, and cut around with a knife to take off any excess dough. you may want to add some dough back, however, additional excess dough will be set aside and you will ultimately have enough excess dough for a sixth pop-tart.
once the dough is rolled out into a rectangle, place the dough on a parchment paper-lined baking tray. add a couple spoonfuls of apple cinnamon filling.
repeat the same process with the remaining half of the dough, cutting off any excess dough from your rectangle shape and setting it aside with the other excess dough.
now, your top half of dough formed into a rectangle, gently place it atop the apple cinnamon filling, pressing down the corners delicately with your fingers. using a fork, wet the prongs slightly (otherwise the fork may stick to the dough and remove it), and sink the prongs into the edges around the pop tart. using a skewer or toothpick, you can also poke six holes on the top of the pop tart in vertical lines (two columns of three).
repeat this process for the four remaining balls of dough, dividing each into two and creating your rectangle shapes. excess dough will be used for a sixth and final pop-tart at the end.
once you're done making your pop-tarts, the last step, is the egg wash. mix the egg white you set aside earlier with a tbsp water, and using a brush, egg wash the top and edges of the pop tart.
once all the pop tarts are prepared and egg washed on the baking sheet, bake in a preheated oven at 340 for 15 minutes. you can serve these immediately with the frosting recipe below, or allow to cool completely and store in between layers of parchment paper in the fridge or freezer. if you're storing in the freezer or fridge to re-heat later, i definitely recommend baking in the oven for the best experience --bake it in the oven at 330 or lower for 10 minutes at least when re-heating. you can also eat these cold too!!