Preheat oven to 400°.
. Lightly spoon flour and cornmeal into dry measuring cups; level with a knife. Combine flour, cornmeal, sugar, and baking soda in a medium bowl; stir well with a whisk. Combine buttermilk and next 6 ingredients in a bowl; stir well with a whisk. Add to flour mixture, stirring just until moist. Spoon batter into 12 muffin cups coated with cooking spray.
. Bake at 400° for 18 minutes or until muffins spring back when touched lightly in center. Remove muffins from pan immediately; place on a wire rack.