Preheat your oven to 375 degrees F. Line a baking sheet with parchment paper. Set aside.
In a medium size mixing bowl, whisk together the flour, cream of tartar, baking soda, and salt. Set aside.
In a medium saucepan, cook the butter over medium heat until brown specs form. (See blog post above for more details).
In the bowl of an electric mixer, fitted with the paddle attachment, beat the brown butter ,1 1/4 cups granulated sugar and brown sugar on medium-high speed until smooth, about two minutes.
Mix in the eggs and vanilla and stir until well combined
With the mixer on low, add the flour mixture and stir until combined.
With a 1.5 inch cookie scoop (about 1.2 ounces), scoop cookie dough and roll into balls.
Stir together the 1/4 cup granulated sugar and cinnamon in a small bowl.
Roll each cookie dough ball in the cinnamon sugar mixture and place onto the baking sheet about 3 inches apart.
Bake the cookies for 9 to 10 minutes. They may look slightly underdone, but once they cool completely, they'll have a soft and chewy center.