Preheat oven to 375°F (190°C). Line baking sheets with parchment paper.

In a medium bowl, whisk together flour, cream of tartar, baking soda, and salt.

In a large bowl, cream butter and sugar until light and fluffy.

Add eggs and vanilla extract, mixing until well combined.

Gradually add dry ingredients to the wet mixture and mix until a soft dough forms.

In a small bowl, mix sugar and cinnamon for the coating.

Roll dough into 1-inch balls and coat each ball in cinnamon sugar.

Place dough balls 2 inches apart on prepared baking sheets.

Bake for 9–11 minutes, until edges are set and centers remain soft.

Cool on the baking sheet for 5 minutes, then transfer to a wire rack.