Preheat oven to 375 degrees. Line two baking sheets with parchment paper or silicone mats.
To make the topping, combine 1/4 cup sugar and a tablespoon cinnamon in a shallow dish. Set aside. In a medium bowl, whisk together flour, cream of tartar, baking soda, and salt.
In an electric mixer with the paddle attachment at medium speed, or using a hand mixer, beat butter, shortening, and remaining 1 1/2 cups sugar together until pale and fully, about 3 to 5 minutes.
Beat in the eggs, one at a time, until evenly incorporated. Scrape down the bowl and beaters as necessary.
Reduce speed to low and add flour mixture slowly until just combined, about 30 seconds. Stir by hand for a few strokes to ensure flour is incorporated.
Working with 1 heaping tablespoon of dough at a time, roll dough into 1 1/2-inch balls, then drop into the cinnamon-sugar mixture and toss to coat. Lay on prepared baking sheets about 2 inches apart. (I use the OXO medium cookie scoop, a size 40 portioner, and do 12 scoops of dough per baking sheet).
Bake the cookies, one sheet at a time, until the edges are starting to brown but the centers are soft and puffy, about 10 to 12 minutes, rotating sheet after 5 minutes. (The cookies will look raw).
Cool cookies on baking sheet 10 minutes, then serve or transfer to cooling racks to cool completely.