Preheat oven to 350º F.

Using an electric stand mixer or a hand mixer cream together butter, brown sugar, and sugar until light and fluffy, approximately 2-3 minutes.

Add eggs and vanilla and beat until well combined and the egg is fully incorporated.

In a separate bowl whisk together flour, cornstarch, cinnamon, baking powder, baking soda and salt. Add to the butter mixture, mixing until it just forms a dough.

In a small bowl mix together the sugar and cinnamon for the coating. Reserve any unused coating mixture.

Scoop into balls of dough, and roll through the cinnamon and sugar mixture into coated evenly. Place on a baking sheet about 2 inches apart.

Bake for about 10 minutes, until the edges are set and the cookies have puffed up. Remove from the oven and let them cool for about 5 minutes before removing to a wire rack to cool completely.

Once the cookies have cooled completely, prepare the frosting. Beat together the butter, both sugars, cinnamon and vanilla until it comes together. Slowly stream in the milk until you get a spreadable consistency.

Top the cookies with frosting, using a knife or pipe onto the cookies (you can use a sturdy zip top bag and cut off the end) if desired. Sprinkle the remaining coating mixture over the top of the freshly frosted cookies.

Let the frosting set up before serving.