Preheat oven to 325°F and grease two 8 1/2 x 4 1/2 loaf pans generously with butter. Set aside.
In a mixing bowl with a hand mixer or stand mixer, beat butter and sugar together. Add the eggs, combine well, then add sour cream, mashed bananas, and vanilla. Stir to combine.
Add the flour, salt, cinnamon, and baking soda to the batter then stir until just combined. Do not overmix.
In a separate bowl, add the washed and completely dried blueberries. Once dry, sprinkle in a small amount of flour, and stir to coat the blueberries completely. Once fully coated, discard the excess flour.
Add the flour-coated blueberries to the batter and gently fold to combine.
Separate the batter evenly between pans. Bake for approximately 1 hour or until a toothpick inserted in the center of the loaves comes out clean.**
Remove from the oven and place on wire cooling rack to cool for at least 20 minutes. Then if desired remove from pan and allow to cool completely. Alternately bread can be kept in pan, cutting out slices as you use them.