Preheat oven to 350 degrees F. Butter either three to four mini loaf pans, or one to two regular loaf pans.
In a medium bowl, mix dry ingredients well. In a small bowl, mash bananas, then add remaining ingredients and mix well.
Pour banana mash into dry mix and combine until moist. Fold in walnuts, if using. Pour batter into loaf pans, about one-third to halfway full.
Bake 40 minutes, or until a toothpick comes out clean. Place pans on a wire rack to cool completely.