Preheat oven to 400ºF.  Grease 12 standard muffin wells or line with paper baking cups. 

Whisk together flours, cinnamon, baking powder and salt in a medium mixing bowl.  Set aside.

Combine mashed bananas, brown sugar, eggs, oil and vanilla in a separate large bowl.  Add flour mixture and stir until flour is moistened.  Fold in nuts, if desired. 

Portion batter into prepared muffins cups, filling each almost full. 

Bake 20 to 25 minutes or until a wooden pick inserted in the center comes out clean.  Transfer muffins to a wire rack to cool.