Preheat the oven to 350℉. Spray three 8x5 inch loaf pans with nonstick spray.
Use an electric mixer to combine the butter and sugar in a large bowl. Blend in the eggs, banana, sour cream and vanilla.
In a separate bowl, whisk together the flour, baking soda, cinnamon and salt. Add to the wet ingredients and mix until incorporated. Divide the batter between the prepared pans.
Bake for 50 to 60 minutes, or until a toothpick inserted into the center comes out clean. Watch the tops while baking, and place a piece of foil on top of the loaves if they are getting too brown.
Let the loaves cool a bit, then turn out onto a rack to cool completely.