In a separate bowl, sift together 2 ¾ cups flour, 2 teaspoons cream of tartar, 1 teaspoon baking soda, and ¼ teaspoon salt.

Add the dry mixture to the butter mixture and stir until a soft cookie dough forms.

In a small bowl, mix ¼ cup sugar with 1 tablespoon cinnamon to make the cinnamon sugar.

Roll the cookie dough into walnut-sized balls, then roll each ball in the cinnamon sugar until completely coated.

Place the coated dough balls on a plate or tray and chill for at least 2 hours. Overnight chilling also works perfectly. (Or, if you prefer a flatter cookie or don't have a lot of time, you can skip chilling.)

When ready to bake, preheat the oven to 400°F.

Arrange the chilled dough balls on an ungreased baking sheet, leaving at least 2 inches of space for spreading.

Bake for 8 to 10 minutes, or until the edges are lightly golden and the centers look set. (We find 9 minutes and 30 seconds in the sweet spot.)

Allow the cookies to cool on the baking sheet for a minute, then move them to a wire rack to finish cooling.