In a large mixing bowl, whisk the melted butter, mashed bananas, and eggs together.
Add the sugar, sour cream, sourdough starter discard, and vanilla. Stir until combined.
Sift in the remaining dry ingredients: flour, salt, cinnamon, baking powder, and baking soda. Mix with a spatula just until combined.
Gently fold in add-ins of choice, such as walnuts or raisins.
Transfer the batter into a prepared loaf pan. Bake at 350 F for 45-60 minutes, or until a toothpick inserted in the middle comes out clean. The top and the sides should be golden in color.