Prep the oven and pan. Heat the oven to 350°F. Line a 9 x 9-inch baking pan with parchment paper.
Mix. In a large mixing bowl, whisk together the melted butter and sugars until combined. Add the eggs and vanilla extract and whisk until combined. Add the flour, cinnamon, cream of tartar, baking powder, salt, and stir until evenly combined. Use a spatula to gently fold in the chocolate chips until evenly combined.
Arrange in pan. Press the dough evenly into the prepared baking pan. Sprinkle a few extra white chocolate chips evenly on top of the dough, if desired, then sprinkle the dough evenly with the cinnamon sugar topping.
Bake. Bake for 30 minutes or until a toothpick inserted in the center comes out mostly clean. Transfer the pan to a wire rack and let the blondies cool for at least 20 minutes before slicing.