Preheat your oven to 350 degrees
Mix the mashed bananas with the warm melted butter, the warm butter helps brake down the banana into a soother consistency.
Stir in the sourdough starter, sugar, vanilla, and egg.
Fold in the flour, baking soda, baking powder, and salt gently until combined. Do not over-mix.
Carefully mix in any nuts or chocolate chips ( optional) if you choose to add any.
Place the batter into a greased standard-size loaf pan, and bake for 1 hour or until the internal temperature is at least 190 degrees. You may need to add more time.
Store in an air-tight container or plastic baggie on the countertop for 3-4 days or in the refrigerator for up to a week. You can also freeze banana bread for up to 3 months.