Preheat oven to 350 degrees. Coat a loaf pan with nonstick cooking spray.
In a large bowl, beat butter, vanilla and sugar with a handheld electric mixer until light and fluffy. Beat in eggs. (Alternatively, do this step in a stand mixer fitted with the paddle attachment.)
In a medium-sized bowl, mix flour, salt and baking soda.
In a separate bowl, mash the bananas and sour cream together.
Using a mixing spoon, blend flour mixture into the creamed mixture alternately with the mashed bananas. Pour into the prepared loaf pan.
Bake for 1hr 10min or until cake tester inserted in the center comes out clean.
Cool to room temperature on a wire rack before removing from pan.