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

Cream butter and 1 1/2 cups sugar until light, then beat in eggs one at a time.

Whisk flour, cream of tartar, baking soda, and salt; add to wet mixture until just combined.

Mix 3 tbsp sugar with cinnamon in a shallow bowl. Scoop dough by tablespoons, roll into balls, then coat in cinnamon sugar.

Place 2 inches apart and bake 8–10 minutes until edges set but centers are soft. Cool slightly on sheet before transferring to a rack.