Cream Butter and Sugar: In a large mixing bowl, beat the softened butter and sugar together until light and fluffy, about 2–3 minutes.
Add Eggs and Vanilla: Mix in the eggs one at a time, then stir in the vanilla until well combined.
Combine Dry Ingredients: In a separate bowl, whisk together flour, cream of tartar, baking soda, and salt.
Mix the Dough: Gradually add the dry ingredients to the wet mixture, mixing just until combined. The dough should be soft but not sticky.
Chill (Optional but Recommended): For thicker cookies with less spread, cover the dough and refrigerate for 30 minutes.
Preheat Oven: Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper.
Prepare Cinnamon-Sugar Coating: In a small bowl, mix together the ¼ cup sugar and cinnamon.
Shape and Roll: Scoop tablespoon-sized portions of dough, roll into balls, and coat thoroughly in the cinnamon-sugar mixture.
Bake: Place dough balls 2 inches apart on the prepared baking sheets. Bake for 8–10 minutes, until edges are set but centers look slightly soft.
Cool and Enjoy: Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack.