Lightly spoon flour into dry measuring cups; level with a knife. Combine flour and next 4 ingredients (flour through salt) in a large bowl; make a well in center of mixture. Combine buttermilk and next 6 ingredients (buttermilk through egg) in a bowl; add to flour mixture. Stir just until moist. Spoon batter into 12 muffin cups coated with cooking spray, and sprinkle evenly with 1 tablespoon sugar.
Bake at 400° for 18 minutes or until lightly browned. Remove muffins from pans; cool on a wire rack.