Preheat oven to 350°F (176°C) and lightly grease a 9" x 5" loaf pan.

Whisk the flour, salt, baking powder, and baking soda together in a bowl and set aside. In a separate bowl mash the bananas with a fork until smooth and set aside.

In a third bowl, melt the butter in the microwave. To the melted butter add the brown sugar, eggs, sourdough starter discard, vanilla extract, sour cream, and mashed bananas and stir them with a spatula until the mixture is smooth.

Add the wet and dry ingredients together and stir until just combined. (Do not over mix!) If adding walnuts, gently fold them into the batter with a spatula.

Pour the batter into the loaf pan and bake for 50-60 minutes or until a toothpick inserted into the center comes out clean.

Allow the banana bread to cool in the loaf pan for 15 minutes. Next, gently run a knife along the inside of the pan to help release the loaf. Carefully transfer it onto a wire rack. Let the loaf rest on the cooling rack until it cools down, making it easier to handle and allowing it to set slightly before you slice it.