In a bowl, combine the first six ingredients. In a small bowl, beat the egg, buttermilk and oil. Stir into dry ingredients just until moistened. Fold in apple, carrots and walnuts. Fill paper-lined muffin cups or cups coated with cooking spray three-fourths full. Bake at 400° for 20-23 minutes or until a toothpick comes out clean. Cool for 5 minutes before removing from pan to a wire rack. Serve warm.