Instructions

• Preheat the Oven - Set the oven rack to the center position and preheat to 375ºF (191ºC). Line two baking sheets with parchment paper.
• Prepare the Dry Ingredients - In a medium bowl, whisk together flour, cream of tartar, baking soda, and salt. Set aside.
• Cream Butter and Sugar - Fit a stand mixer with the paddle attachment or use a hand mixer. On medium speed (setting 5), beat the butter, shortening, and 1 ½ cups of sugar until pale and fluffy, 3 minutes.
• Incorporate the Eggs - Add the eggs, one at a time to the butter mixture. Mix on medium speed until incorporated, 30 seconds. Scrape the sides of the bowl in between addition.
• Add the Dry Ingredients - Turn the mixer to the lowest setting and slowly add in the flour. Mix until just combined, and the dough feels stiff, about 30 seconds. Stir the dough with a spatula to incorporate any flour pockets, but do not overmix.
• Roll the Dough Balls - In a small bowl, combine ¼ cup sugar and cinnamon. Make 2 tablespoons (30g, 1 ounce) sized cookie dough balls, then roll them into the mixture to completely coat the outside. Repeat with the remaining dough.
• Bake the Cookies - Stagger the balls 3" apart on the baking sheets, about 9 to 12 per sheet. Bake 1 sheet at a time until the edges are set and beginning to brown, about 10 to 12 minutes, rotating halfway through. The centers should be puffy, soft, and cracked and look slightly raw in the cracks.
• Cool After Baking - Cool the cookies on the baking sheet for 10 minutes then transfer them to a cooling rack.