Preheat oven to 350 F. Prepare thawed or homemade pie crust in pie dish and set aside. Stir cinnamon, sugar and butter and brush all over crust.
To prepare the syrup: Place brown sugar, water, corn syrup and butter in saucepan. Over medium heat, bring to a boil, stirring until sugar is dissolved (about 2 minutes). Remove from heat, stir in vanilla and set aside.
For the filling: Beat butter in a stand mixer until creamy (about 1 minute). Add in sugar, powdered sugar, baking powder, salt and cream of tartar until smooth. Add egg and vanilla, followed by milk until combined. Lastly, gently beat in the flour.
Pour filling into pie crust. Top with syrup. Add another sprinkle of cinnamon and sugar if you'd like an extra sweet kick. ;)
Cover pie with a folded piece of foil (it will look like a little tent) and bake for 25 minutes. Remove foil and cook for another 20 minutes. Check for doneness with a toothpick inserted in the center that comes out clean. Remove from oven and place on a wire rack to cool for about an hour before adding glaze.
To make glaze: combine all glaze ingredients until smooth. Add more milk for a more runny consistency or more sugar for a thicker glaze. Once pie is cooled, drizzle over the top and enjoy!