Preheat oven to 350°.  Grease and flour loaf pan or you can use Bakers Joy. 

Cream butter and sugar well.  While this is being done, combine your flour, baking powder, baking soda and salt in a bowl.  Once the butter and sugar are creamed, then add beaten eggs and vanilla.  Blend in the flour, three tblsp. at a time, mixing well.  Once the flour has been mixed in, then add in the milk.  Once this is all incorporated, turn off your mixer and stir in the mashed banana and/or nuts.

Bake in a preheated oven for approximately 60 minutes.