Combine the dry ingredients: flour, cream of tartar, baking & salt into a bowl. Give the ingredients a quick whisk to mix them together, set the bowl aside.
In a separate, large mixing bowl combine the butter and sugar together. Using a handheld mixer or a stand mixer with a paddle attachment, cream the butter and sugar together for 2 to 3 minutes on medium speed. Scrap down the sides of the bowl and add in the eggs and vanilla extract, continue to mix the ingredients together until combined. Slowly add in the dry ingredients, mixing on low speed just until the cookie dough forms.
Chill the cookie dough: Line a baking sheet with parchment paper and use a cookie scoop to roll out balls of cookie dough, placing them on the baking sheet. Cover the cookie dough with plastic wrap and place in the refrigerator to chill* for 4 to 6 hours or up to over night.
When your ready to bake the cookies preheat oven to 400 degrees. Line a baking sheet with parchment paper or lightly spray with non-stick cooking spray. Remove cookie dough from fridge and assemble the cinnamon sugar mixture on a plate or in a shallow bowl. Double roll each cookie in the cinnamon sugar mixture and place them on a baking sheets, about an inch apart. Bake for 7 minutes, no more, no less! Cookies will look slightly underbaked (this is fine!) as they will bake a little longer as they cool. Allow cookies to cool for 10 minutes before serving.