Over medium heat, mix pumpkin puree, brown sugar, cinnamon, nutmeg, ginger and all spice together with egg until well combined. About 3 minutes.
Roll out pie crust and use a pizza roller to cut it into strips about 2 inches wide. Place about one tablespoon of filling every two inches.
Put pie crust over the filling and cut into rectangles.
Use a fork to press edges closed. It's ok if some filling squeezes out. Place mini pop-tarts onto baking sheet lined with foil or parchment paper or sprayed with non-stick spray. Bake for 10 minutes at 350 degrees or until edges are just browned. I bake way more on my pizza stone than just pizza, including these pop-tarts! Plus, I think it makes a great background for styling for photos or serving at parties at my house.
While the pop-tarts are baking, make the frosting. Whisk together the powdered sugar and whipping cream. If the mixture is dry, add one tablespoon of additional cream or almond milk until the frosting is thick but well combined. You might need to take a few extra stirs before adding additional liquid. You don't want to add too much or the icing will be too runny.
Let pop-tarts cool completely, then dollop the frosting on top of the little tarts. Add sprinkles and let cool for an hour so that frosting will harden.