Preheat the oven to 350º F
Grease and flour two 9x5 inch loaf pans.
Sift the flour into a large bowl.
In a separate bowl, mix together the butter or margarine and sugar until smooth. Stir in the bananas, eggs, and walnuts until well blended. Pour the wet ingredients into the dry mixture and stir just until blended.
Divide the batter evenly between the two loaf pans.
Bake for 60 to 70 minutes in the preheated oven, until a knife inserted into the crown of the loaf comes out clean.
Let the loaves cool in the pans for at least 5 minutes, then turn out onto a cooling rack, and cool completely.
Wrap in aluminum foil to keep in the moisture.