Chop the walnuts and reserve 1 tbsp for sprinkling on top.
Add sugar and melted butter.
Mix the dry ingredients really well or sift and then add to banana mixture [ Mixing dry ingredients is important. Otherwise you will be biting into lumps of uncooked baking powder not a pleasant taste!].
Add the chopped nuts.
Mix just enough to bring everything together.
Fill muffin cups about 3/4 to the top.
Sprinkle with chopped walnuts.
Bake for 20 minutes or till the muffins are golden brown.