Preheat the oven to 350 degrees.Line a 9x13" baking dish with parchment paper and spray with nonstick cooking spray.
Mix melted butter, white sugar, brown sugar, and eggs together. Add baking soda, cream of tartar, salt and flour. Mix thoroughly. Pour into the prepared baking dish.
Combine sugar and cinnamon in a small bowl.Sprinkle batter with cinnamon and sugar mixture. Bake 25-30 minutes, or until an inserted toothpick comes out dry.Allow cookie bars to cool in the pan for 30 minutes before slicing.
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Notes
This recipe makes 24 small bars or 12 large. Wrap the baking dish with plastic to keep fresh. Store at room temperature.