prepare 12-cup muffin pan with liners, or spray with a non stick cooking spray, like Pam.
combine dry ingredients in a small bowl.
Using a stand mixer, like a Kitchenaid with the paddle attachment, cream butter, sugar, bananas, egg, flavorings and milk (tip: If you use a Kitchenaid with the paddle attachment, there is no need to soften the butter, or mash the bananas; the mixer will do it for you).
Stir dry ingredients into banana mixture.
Stir in walnut pieces.
Divide batter evenly between muffin cups.
remove when lightly browned and centers are firm to a light touch with your finger tip.