Pre-heat oven to 350 degrees F or 175 degrees C. Grease a bread pan. I use a silicone bread form, which does not require greasing.
In a mixing bowl, mix together the melted butter and sugar. Add the eggs and vanilla, and mix well. If using a kitchen machine, such as a KitchenAid, use the whisk attachment.
If using a kitchen machine, such as a KitchenAid, switch to the mixing attachment. Using a sifter, add in the flour and baking soda, then add in the salt. Mix into the batter until smooth
Now add in the sour cream, walnuts and bananas.
Pour batter into bread form.
Bake at 350 degrees F or 175 degrees C for 60 minutes, or until a toothpick inserted into the center comes out clean. Leave cool for about 10 minutes.