Preheat the Oven: Preheat your oven to 350°F (175°C). Grease or line a 9x13 inch baking pan with parchment paper, leaving some overhang for easy removal.
Cream Butter and Sugar: In a large mixing bowl, beat the softened butter and granulated sugar together until light and fluffy.
Add Eggs and Vanilla: Add in the eggs one at a time, mixing well after each addition. Blend in the vanilla extract.
Combine Dry Ingredients: In a separate bowl, whisk together the flour, cream of tartar and baking soda until thoroughly combined.
Mix Ingredients: Gradually add the dry ingredients to the butter mixture, mixing until just combined.
Spread in Pan: Spread the cookie dough evenly into the prepared baking pan.
Bake: Bake in the preheated oven for about 20-25 minutes, or until the edges are golden and a toothpick inserted into the center comes out clean.
Cinnamon Sugar Topping: In a small bowl, combine brown sugar and cinnamon. Sprinkle this mixture evenly over the top of the dough. Once cooled, cut into squares.
Enjoy your homemade snickerdoodle bars with a glass of milk or a cup of coffee!