Brown Sugar Cinnamon Poptart Bars

Preheat your oven to 350F. In a large bowl, combine your butter, brown sugar, and powder sugar. Mix until creamed together, either by hand or with a stand/power mixer. Add in your egg and vanilla and mix again. Add in your flour and cinnamon and mix until a dough forms; keep mixing even if it seems dry at first. Split your dough in half. Press one half into a lined 8x8 baking dish until flat. Take the other half of the dough and press it into an 8x8 square on a piece of parchment paper. To make the brown sugar cinnamon filling, mix all filling ingredients in a small bowl. Add this filling to your 8x8 baking dish, then top with the other half of your dough (from the parchment paper). Bake in the oven at 350F for 40 minutes. Allow your poptart to cool for 15 minutes before icing them. To make the icing, combine powder sugar, vanilla, cinnamon, and milk. Spread over cooled poptart bars. Enjoy!