Preheat your oven to 350°F.
Grease a 9x5x3-inch loaf pan with non-stick spray or a bit of butter.
In a large mixing bowl, cream the softened butter and sugar until the mixture is light and fluffy.
Add the eggs, one at a time, beating well after each addition.
In a separate bowl, whisk together the flour, baking soda, and salt until they are well combined.
Add the dry ingredients to the butter mixture, alternating with the mashed bananas and sour cream.
Stir in the vanilla extract.
Mix just until the batter is smooth.
Pour the batter into the prepared loaf pan.
Bake in the preheated oven for about 60 minutes, or until a toothpick inserted in the center comes out clean.