In a small bowl, whisk together the 1/4 cup granulated sugar and 2 tablespoons ground cinnamon until well combined. Set aside.

In a medium bowl, whisk together the all-purpose flour, cream of tartar, baking soda, and salt. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment (or using a large bowl and a hand mixer), cream together the softened unsalted butter and 1 1/2 cups granulated sugar on medium-high speed until light and fluffy, about 2-3 minutes. Scrape down the sides of the bowl as needed.

Add the eggs one at a time, mixing well after each addition. Beat in the vanilla extract until just combined.

Gradually add the dry ingredient mixture to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix; stop as soon as no streaks of flour remain.

Cover the dough with plastic wrap and chill in the refrigerator for at least 30 minutes, or up to 2 hours. Chilling helps prevent spreading and enhances chewiness.

While the dough chills, preheat your oven to 375°F (190°C). Line two large baking sheets with parchment paper.

Scoop rounded tablespoons of dough (about 1.5-2 tablespoons each) and roll them into smooth balls. Roll each dough ball generously in the prepared cinnamon sugar coating until fully covered.

Place the coated dough balls about 2 inches apart on the prepared baking sheets. Bake for 8-10 minutes, or until the edges are set and lightly golden, but the centers still look very soft and slightly puffed. Do not overbake!

Remove the baking sheets from the oven and let the cookies cool on the sheets for 5 minutes before transferring them to a wire rack to cool completely. The cookies will firm up as they cool. Repeat with remaining dough.