Preheat oven to 350°F (175°C) and grease a 9x5 inch loaf pan.
Mash bananas in a large bowl until mostly smooth.
Whisk in melted butter, sugar, egg, sour cream, and vanilla.
Sprinkle baking soda and salt over the mixture and stir in.
Fold in flour just until no dry streaks remain.
Fold in nuts or chocolate chips if using.
Pour batter into the prepared pan and smooth the top.
Bake 55 to 60 minutes, until a toothpick comes out with a few moist crumbs.
Cool in the pan for 10 minutes, then transfer to a wire rack to cool fully before slicing.