Prepare the Cookie Bar Dough

1. Preheat the Oven: Preheat your oven to 350°F (175°C). Grease or line a 9×13-inch baking pan with parchment paper.
2. Combine Wet Ingredients: In a large mixing bowl, whisk together the melted butter and granulated sugar until smooth. Add the eggs and vanilla extract, mixing until fully combined.
3. Mix Dry Ingredients: In a separate bowl, whisk together the flour, cream of tartar, baking soda, and salt.
4. Combine Wet and Dry Mixtures: Gradually add the dry ingredients to the wet mixture, stirring until just combined. Be careful not to overmix.

Assemble and Bake

1. Spread the Dough: Evenly press the dough into the prepared baking pan, smoothing the top with a spatula.
2. Add the Topping: In a small bowl, mix the 2 tablespoons of granulated sugar with 1 teaspoon of ground cinnamon. Sprinkle this mixture evenly over the top of the dough.
3. Bake: Bake in the preheated oven for 25-30 minutes or until the edges are golden and a toothpick inserted into the center comes out clean.
4. Cool: Let the bars cool in the pan on a wire rack for at least 20 minutes before cutting into squares.

Serve and Enjoy

1. Cut and Serve: Cut the bars into 16 squares and serve them warm or at room temperature.