In a medium bowl, whisk together the flour, cream of tartar, baking soda, and salt and set aside.
In a large bowl, using an electric mixer fitted with a paddle or whisk attachment, cream the butter, sugar, and brown sugar on medium-high speed until light and creamy, about 2-3 minutes. Then, add the egg and vanilla and mix until well combined, about 1 minute. Add the flour mixture and mix on low speed just until combined, about 30-60 seconds. Cover and chill in the fridge for 2 hours.
Preheat the oven to 350°F (175°C). Line 2-3 baking sheets with parchment paper and set aside.
In a small bowl, combine the granulated sugar and cinnamon. Then scoop 12 equal-sized balls (about 2 tablespoons [40g] each) of cookie dough, roll into even balls with your hands, and roll in the sugar coating mixture to cover them entirely.
Place the cookies about 3 inches (7.5 cm) apart on the prepared baking sheets. Bake one sheet at a time for 8 to 9 minutes, or until the edges are set and lightly browned and the centers look puffy, dry, pale, and underbaked. Remove from the oven and let cool on the baking sheet for about 5-10 minutes (they will continue baking) or until firm enough to move. Then, transfer to a wire rack and let cool completely. The cookies will stay fresh and soft in an airtight container at room temperature for up to 5 days or freeze for up to 3 months.