Step 1

Preheat the oven to 375°F. Line 2 baking sheets with parchment paper.

Step 2

In a large bowl, whisk together the flour, cream of tartar, baking soda, and salt until thoroughly combined. Set aside.

Step 3

In the bowl of a stand mixer fitted with the paddle attachment, combine the butter, brown sugar, and 1¼ cups of the granulated sugar. Beat on medium-high speed until light and fluffy, 3 to 5 minutes. Scrape down the sides of the bowl, then beat in the eggs, 1 at a time, on medium speed. Beat in the vanilla. Scrape down the sides of the bowl again. With the mixer on low speed, slowly add the dry ingredients and beat until combined.

Step 4

In a medium bowl, whisk together the cinnamon and the remaining 6 tablespoons granulated sugar. Using a 2-tablespoon cookie scoop, form balls of dough and gently roll them in the cinnamon sugar, coating generously. Transfer to the prepared baking sheets, spacing the dough balls about 3 inches apart.

Step 5

Bake in batches, rotating the pans halfway through, until puffed and just barely set in the center, 8 to 10 minutes (the cookies will continue to set as they cool). Let the cookies cool on the baking sheets for 5 minutes before transferring to wire racks to cool completely.