Lightly spoon flour into a dry measuring cup, and level with a knife.
Combine flour and next 5 ingredients (flour through baking soda) in a large bowl, and make a well in center of mixture.
Combine buttermilk and next 4 ingredients (buttermilk through egg) in a bowl; add to flour mixture. Stir just until moist. Spoon batter into an 8-inch square baking pan coated with cooking spray.
Bake at 425 for 20 minutes or until a wooden pick inserted in center comes out clean.