In a mixing bowl, cream together the butter and sugar until smooth. Add in the eggs and mix until combined. In a separate bowl, dissolve the baking soda into the sour cream and let sit for a minute. Add this mixture to the butter/egg mixture and mix slightly. Mash the bananas in a separate bowl and then add to the batter. Add the flour, vanilla and salt to the rest of the batter and mix until combined (don't over mix). Grease 2 bread pans with butter spray or shortening and then dust with flour. Pour half of the batter into each pan and cook at 350 for 1 hour and 10 minutes (or until toothpick comes out clean). Check at 1 hour and see how much longer is needed.
Notes
Do you ever have bananas on your counter that are too dark and ripe to eat, and you feel badly throwing them away. These are PERFECT banana bread bananas. If you don't have time to make banana bread right away, peel the banana and put it in a ziploc bag to freeze. I keep a zip loc bag with ripe bananas in my freezer at all times. When you are ready to bake, pull them out, microwave or let them thaw and you will have delicious banana bread in about an hour. You know the saying..waste not, want not :)