In your mixer, using the paddle attachment, cream together the melted butter and sugar on high for 30 seconds. Add in egg and bourbon, mix for another 30 seconds
In a separate bowl, mix flour, cream of tartar, and salt.
Fold in dry ingredients into the wet ingredients. Mix until well combined. Then add the batter to the prepared 8x8 pan.
Mix together the additional Sugar and Cinnamon and sprinkle on top of the batter.
Bake 30-35 minutes.
Allow to cool completely before cutting into squares. Enjoy