Preheat your oven to 375°F (190°C). Line two baking sheets with parchment paper or silicone mats. In a medium bowl, whisk together the flour, cream of tartar, baking soda, and salt.

In a large mixing bowl, beat the softened butter and sugar until light and fluffy. Gradually add the eggs one at a time, followed by the vanilla extract.

Slowly incorporate the dry ingredients into the wet mixture, stirring just until combined. Chill the dough for 15 minutes if needed.

Mix the remaining sugar and cinnamon in a small bowl. Scoop out tablespoon-sized dough portions, roll into balls, and coat in the cinnamon-sugar mixture.

Bake for 8-10 minutes, until the edges are set but centers are slightly soft. Let them rest for 5 minutes on the baking sheet.