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["Place a rack in the upper-middle position of the oven.", "Preheat oven to 325F.", "In a bowl, combine white sugar, brown sugar, salt and cinnamon, mixing well with your fingers until there are no lumps.", "Add melted butter and stir until smooth.", "Stir in cake flour until fully combined.", "Set aside at room temperature, covered with plastic wrap, to allow the gluten to relax, 10-15 minutes.", "In work bowl of a standing mixer, combine flour, sugar, salt and baking soda using the paddle.", "(If you don't have a stand mixer, whisk together in a large bowl.)", "With the mixer running on medium-low, add the butter 1 tablespoon at a time, waiting until each piece breaks down before adding the next.", "Continue mixing until it has a uniform sandy texture.", "(If working by hand, cut butter in with pastry cutter until very fine.", ").", "Add the vanilla, buttermilk, egg and egg yolk.", "Run mixer on medium-high until batter is smooth and thick, at least 1 minute, or use a handheld electric mixer.", "The batter will be very thick, almost like frosting.", "Spray an 8""-square baking pan with non-stick spray.", "Cut a piece of parchment paper 16"" by 7 1/2"
