Preheat the oven to 350°F. Liberally spray a 13x9-inch baking pan with nonstick cooking spray. Set aside.
In a medium bowl, use a whisk to sift together flour, cream of tarter, baking soda salt and nutmeg.
Using an electric mixer on medium high speed cream together granulated sugar, powdered sugar and butter with vanilla for 2 minutes or until fully combined.
Add the eggs one at a time beating well after each addition. Stop and scrape the bowl occasionally.
Lower the speed of the mixer and gradually add the sifted dry ingredients. After all has been added, increase to medium-high beating just until fully incorporated. Press cookie dough in an even layer in the pan.
In a small bowl, mix together granulated sugar and cinnamon. Sprinkle evenly over the top of the bars.
Bake for 25-30 minutes or until a toothpick inserted into the center shows moist crumbs.
Cool in the pan on a cooling rack. Store leftovers in an airtight container at chilled for up to 4 days or at room temperature for 2-3 days.
Notes
Sugar: In developing this recipe, I chose to use a combination of granulated and powdered sugar (confectioners sugar) for the dough. Combining the two lends a tender crumb to the finished product. The powdered sugar gives a melt-in-your-mouth texture to the cookies bars that makes them irresistible. You could use all granulated sugar, in a pinch.
Adjust the Cinnamon: When mixing the cinnamon sugar topping start with 2 teaspoons and taste. Use as is or add more cinnamon to your taste.
Flour: You could adapt this recipe using gluten free flour.
Sugar: This recipe works best using white sugar. Brown sugar would give it more of a molasses flavor.
Line the Pan with Parchment Paper: If you'd like to be able to remove the chewy snickerdoodle bars from the pan for slicing, line the pan with parchment paper first. Leave a 2-inch overhang to form handles to life the bars from the pan in one fell swoop.