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

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

3. In a large bowl, beat softened butter and 1 1/2 cups granulated sugar until light and fluffy (2–3 minutes).

4. Add eggs and vanilla extract. Beat until combined and smooth.

5. Gradually mix in the dry ingredients until a soft dough forms.

6. In a small bowl, mix 1/4 cup granulated sugar with 2 teaspoons ground cinnamon.

7. Scoop dough into 1-tablespoon-sized balls and roll in cinnamon sugar mixture.

8. Optionally, dip tops in red or green sanding sugar for a festive look.

9. Place on baking sheets, spacing 2 inches apart.

10. Bake for 9–10 minutes or until edges are set and centers look slightly underbaked.

11. Let cool on the baking sheet for 5 minutes, then transfer to a wire rack.