Preheat the oven to 375°F. Line two baking sheets with parchment paper and set aside.
In a medium bowl, whisk together the flour, cream of tartar, baking soda, and salt. Set the dry ingredients aside.
In a large mixing bowl, beat the softened butter and granulated sugar until light and creamy.
Add the eggs and vanilla extract. Beat until smooth and fully combined, scraping down the sides of the bowl as needed.
Gradually add the dry ingredients to the wet mixture. Mix just until a soft cookie dough forms. Avoid overmixing.
In a small bowl, combine the granulated sugar and ground cinnamon for the coating.
Scoop portions of dough and gently roll them between your hands to form balls. Roll each dough ball generously in the cinnamon-sugar mixture.
Place the coated dough balls on the prepared baking sheets, leaving enough space between them for the cookies to spread.
Bake for about 9–10 minutes, or until the edges are set and the centers still look slightly soft.
Allow the cookies to cool on the baking sheet for a few minutes, then transfer them to a wire rack to cool completely.
Serve warm or at room temperature with milk, coffee, tea, or your favorite dessert.