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 six equal rectangles, to form the pop-tart crust. Reserve the edges you cut off. Repeat with second crust, and re-roll the edges to get 2-4 more rectangles.
Lay out your crust rectangles on a flat surface. Place 1 tablespoon of applesauce 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 a cookie sheet lined with parchment or a silpat. 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 brown sugar, corn syrup, vanilla, and milk. Spoon over the pop-tarts and sprinkle with sprinkles.
Pop-tarts can be reheated in the microwave or frozen for later eating. Do not toast frosted pop-tarts. You can omit the frosting if you want to toast them to reheat.