Preheat oven to 425°F. Line a cookie sheet with parchment paper or silicone baking mats.
Open your can of pie filling and use kitchen scissors to slice the apples inside the can (so they're more bite size).
Unroll one pie crust. Use a rolling pin to roll the circle into more of a rectangle shape. Use a knife to cut off the rounded edges, to give you an exact rectangle. Cut the rectangle into 6 equal rectangles, to form the pop-tart crust. Reserve the edges you cut off. Repeat with second crust.
Lay out your crust rectangles on a flat surface. Place 1 tablespoon of apple pie filling in the center of half of them.
Whisk egg in a small bowl. Use your finger and trace the edges of each of the rectangles containing applesauce with a bit of egg, to help in sealing the pop-tart. Cover the applesauce rectangles with a plain one and seal the edges together with the tines of a fork.
Place pop-tarts on prepared baking sheets. Poke each pop-tart with a fork a few times so that air can escape while baking, so they don’t exapnd. Bake for about 13-15 minutes, until golden brown. Cool.
Make the frosting by whisking together the powdered sugar and cinnamon and then adding 1 tablespoon milk. Whisk while adding more milk slowly, until you have a thick glaze. Glaze poptarts.
Store in the refrigerator, these taste best room temperature or warmed. Warm on 50% power in 15 second increments in the microwave so as not to liquify the frosting. Do not toast, but you can warm them in a toaster oven. Freeze in a single layer for up to 3 months.