1cup(226 g or 2 sticks) unsalted butter, room temperature
1 ½cups(300 g) granulated sugar
2large eggs, room temperature
2teaspoonspure vanilla extract
Cinnamon sugar topping
Preheat oven to 350° F. Grease and flour (or line with parchment paper) a 9x13 baking pan. Set aside.
In a large bowl, whisk together flour, cream of tartar, baking soda, cinnamon and salt. Set aside.
In the bowl of a stand mixer (or using a hand mixer), beat butter and sugar on medium high speed until light and fluffy, about 3 minutes. Add eggs and vanilla and mix until combined. Scrape down the sides and bottom of the bowl as necessary. Add flour mixture and mix just until combined.
Transfer dough to prepared baking pan and press down firmly. In a small bowl, whisk together sugar and cinnamon for the topping. Sprinkle evenly over the dough. It helps to sprinkle from at least a foot above the pan so the cinnamon sugar is dispersed evenly.
Bake snickerdoodle bars at 350° F for 25-28 minutes (don’t over bake). The bars are done when the edges are set and the center is still soft. Let the bars cool completely before cutting and serving.