Preheat your oven to 375° Fahrenheit.
In a large bowl, whisk together flour, baking soda, cream of tartar and salt. Set aside.
In a bowl of a stand mixer fitted with the paddle attachment, add butter, shortening, and sugar and mix on medium high until light and fluffy. About 2-3 minutes
Scrape down the sides and bottom of the bowl. Add eggs, vanilla and milk and mix until fully combined. About 1-2 minutes.
Scrape down the sides and bottom of the bowl and add your dry ingredients slowly. Mix on low until fully combined. Dough should start to clean the sides of your mixing bowl.
Mix your 1/3 C Sugar and tablespoon Ground Cinnamon in a small bowl. Using a regular sized iced cream scoop, drop dough into the cinnamon sugar mixture and roll to cover completely. Then place dough balls at least 2" apart on a cookie sheet lined with parchment or a silicone baking mat.
Bake for 8-10 minutes, until they puff and crack. The cracks will still look underbaked when you remove them. Do NOT overbake.
Cool on sheet for 3-5 minutes and then remove to a wire rack to cool completely.