Preheat the oven: Preheat your oven to 350°F (175°C). Grease a 9x5-inch loaf pan or line it with parchment paper.

Mix Wet Ingredients: In a large bowl, mix the mashed bananas, melted butter, and brown sugar until well combined. Add the eggs, one at a time, followed by the vanilla extract. Stir in the sourdough and discard until smooth.

Combine Dry Ingredients: In a separate bowl, whisk together the flour, baking soda, salt, cinnamon, and nutmeg. Gradually fold the dry ingredients into the wet mixture, being careful not to overmix.

Add Mix-ins: If using, fold in the chopped walnuts or chocolate chips until evenly distributed in the batter.

Bake: Pour the batter into the prepared loaf pan and smooth the top. Bake for 55–65 minutes, or until a toothpick inserted into the center comes out clean.

Cool: Allow the banana bread to cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.

Serve: Slice and enjoy this moist, flavorful sourdough; discard banana bread as a breakfast treat or a delightful snack.