2 teaspoons cream of tartar
1 teaspoon baking soda
1 cup unsalted butter (2 sticks), softened
1 cup packed brown sugar
3/4 cup granulated sugar
2 eggs
1/4 cup buttermilk
1 1/2 teaspoons vanilla extract
2 tablespoons melted butter
Cinnamon & Sugar Topping:
2 teaspoons ground cinnamon
1/2 cup granulated sugar
Preheat oven to 375 degrees F. Line a 9x13” baking dish with parchment paper. Spray with nonstick cooking spray. In a medium bowl, whisk together the flour, cream of tartar and baking soda. Set aside. Cream softened butter, brown sugar and ¾ cup granulated sugar in a large bowl with a hand mixer on medium speed until light and fluffy, about 5 minutes. Add eggs, one at a time, beating on medium speed until blended. Beat in buttermilk and vanilla. Add flour mixture to creamed mixture and beat just until combined. In a separate bowl, whisk together the Cinnamon and Sugar Topping. Sprinkle 2 tablespoons cinnamon sugar in the bottom of prepared dish. Drop half the batter by the spoonfuls evenly over cinnamon sugar then spread into an even layer (its okay if the cinnamon sugar spreads), then . If you are having an extra hard time spreading the batter, then coat a piece of wax paper with nonstick spray and lay it on top of the dough and use your hands to spread out the dough. (thanks to reader Pia for this awesome tip!)Sprinkle 3 more tablespoons cinnamon sugar over dough. Drop remaining dough by spoonfuls over the cinnamon sugar layer (it will be thick). Dip a spatula in the melted butter and carefully spread dough in an even layer, repeatedly dipping spatula in butter as necessary. Sprinkle top with remaining cinnamon and sugar. Bake for 25-30 minutes or until toothpick inserted in the center comes out clean. Let cool completely in the dish, then cut into 24 bars. Cover bars and store at room temperature.