Preheat oven to 350°. Grease a 9 x 5" loaf pan. In a large bowl, stir together the melted butter and sugar. Add the eggs and vanilla, mix well, combine the flour, baking soda and salt, staring into the butter mixture until smooth. Finally, fold in the sour cream, walnuts and bananas. Spread evenly into the prepared pan. Bake at 350°F for 60 minutes, or until a toothpick inserted into the center of the wealth comes out clean. Cool loaf in the pan for 10 minutes before removing to a wire rack to cool completely.