Preheat oven to 350º F (180º C). Grease and flour (or line with parchment paper) a 13x9 pan. Set aside.
In a medium bowl, combine flour, baking powder, baking soda, salt and cream of tartar. Set aside.
In a large bowl, combine melted butter, sugars (white and brown); stir well until well combined.
Add in sour cream, vanilla extract and vinegar; stir until well combined.
Stir dry ingredients into the butter mixture; mix until all the ingredients are incorporated.
Spread batter evenly into prepared 13x9 pan.
Prepare the topping: mix the sugar and cinnamon in a small bowl. Sprinkle evenly over the batter.
Bake for 20 – 25 minutes, or until a toothpick inserted in the center comes out clean. NOTE: For chewy snickerdoodle bars bake for 15 – 20 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.
Cool completely in the pan on a wire rack. Cut into 12 or 24 bars.
Notes
STORE: These Snickerdoodle Bars can be stored at room temperature in an airtight container for about three days or in the refrigerator for up to a week.FREEZE: place the bars in a single layer in a large bag or airtight container between sheets of parchment. Freeze for up to 3 months. Thaw overnight in the refrigerator, then allows coming to room temperature before serving.MAKE AHEAD: These bars can be made three days in advance and kept in an airtight container at room temperature until ready to serve.FOR THICKER SNICKERDOODLE BARS: Prepare the recipe as directed. Bake in a greased 9-inch square baking pan for 35-40 minutes. Cool completely in the pan on a wire rack. Cut into bars.FOR CHEWY SNICKERDOODLE BARS: Prepare the recipe as directed and bake for 15 – 20 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs. Cool completely in the pan on a wire rack. Cut into bars.If you're making this recipe, please read the whole post content to get lots of tips, tricks, variations, frequently asked questions, and step-by-step photos. Also, before you get started, I recommend reading my Beginner’s Guide to Eggless Baking and my FAQs section. ★ Did you make this recipe? Don't forget to give it a star rating below! Please note that nutritional information is a rough estimate, and it can vary depending on the products used.