Preheat the oven to 350°F (175°C). Grease a 9x13-inch baking pan or line it with parchment paper.
In a medium bowl, whisk together the flour, cream of tartar, baking soda, and salt. Set aside.
In a large bowl, cream together the butter, granulated sugar, and brown sugar until light and fluffy, about 2-3 minutes.
Beat in the eggs, one at a time, then add the vanilla extract.
Gradually add the dry ingredients to the wet ingredients, mixing just until combined.
Spread the dough evenly into the prepared baking pan.
In a small bowl, mix together the cinnamon and sugar for the topping. Sprinkle evenly over the dough.
Bake for 25-30 minutes, or until the edges are set and a toothpick inserted in the center comes out clean.
Let cool completely in the pan before cutting into bars.