Preheat oven to 400°.
Combine first 6 ingredients in a large bowl. Stir in apple, and make a well in center of mixture. Combine buttermilk and next 6 ingredients (buttermilk through egg); stir well with a whisk. Add to flour mixture, stirring just until moist. Spoon batter into 18 muffin cups coated with cooking spray.
Combine 3 tablespoons sugar and 2 teaspoons cinnamon; sprinkle evenly over batter. Bake at 400° for 18 minutes or until done. Remove from pans immediately; cool on a wire rack.