Toss sugar with cinnamon in a small bowl. Set aside.
In a large bowl using a hand-held mixer or stand mixer with paddle attachment, cream the softened butter for about 1 minute on medium speed. Get it nice and smooth, then add the sugar on medium speed until fluffy and light in color. Mix in egg and vanilla. Scrape down the sides as needed. Set aside.
In a medium size bowl, whisk together the flour, cream of tartar, baking soda, cinnamon, and salt. With the mixer running on low speed, slowly add the dry ingredients to the wet ingredients in 3 different parts. The dough is quite thick and you may have to stir the rest by hand.
Category: Cookies, Brownies, Cakes