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

2. In a bowl, whisk together flour, cream of tartar, baking soda, and salt. Set aside.

3. In a large bowl, beat butter and sugar together until light and fluffy (about 2–3 minutes).

4. Beat in eggs one at a time, then stir in vanilla.

5. Gradually add dry ingredients to the wet mixture, mixing just until a dough forms.

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

7. Roll the dough into 1-inch (2.5 cm) balls, then roll each in the cinnamon-sugar mixture until coated.

8. Arrange on baking sheets, spacing them about 2 inches apart. Bake for 9–11 minutes, until edges are set and tops slightly cracked.

9. Let cookies rest on the pan for 5 minutes before transferring to a wire rack to cool completely.