Preheat oven to 350°F (175°C) and grease a 9x5-inch loaf pan. Mash the bananas in a large bowl.

Whisk in the melted butter, sugar, eggs, vanilla, and sour cream until smooth.

In a separate bowl, whisk together the flour, baking soda, and salt.

Gently fold the dry ingredients into the wet mixture until just combined, then fold in nuts if using.

Scrape batter into the prepared pan and bake for 55 to 65 minutes, until a toothpick comes out with moist crumbs. Cool in the pan 10 minutes, then transfer to a wire rack to cool completely before slicing.