Start by gathering all your ingredients on the counter. Make sure your bananas are ripe; the more brown spots, the better! Preheat your oven to 350°F (175°C) and grease your loaf pans with a bit of coconut oil or butter.
In a large mixing bowl, combine the melted coconut oil, melted butter, and brown sugar. Whisk until smooth, then add the eggs one at a time, mixing well after each addition. Next, stir in the mashed bananas, maple syrup, vanilla extract, and your unfed sourdough starter. Mix until everything is well combined.
In a separate bowl, whisk together the all-purpose flour, baking soda, baking powder, and kosher salt. This ensures that your leavening agents are evenly distributed throughout the flour before mixing it with the wet ingredients.
Gradually add the dry ingredients to the wet ingredients, using a rubber spatula to gently fold them together. Be careful not to over-mix; it’s okay if there are a few lumps. If you’re adding chocolate chips, butterscotch chips, or nuts, fold them in now.
Divide the batter evenly between the prepared loaf pans. Bake in the preheated oven for about 60-70 minutes or until a toothpick inserted into the center comes out clean. If the tops are browning too quickly, you can tent them with aluminum foil.
Once baked, remove the pans from the oven and let them cool in the pans for about 10 minutes. Then, transfer to a wire rack to cool completely. Slice and serve your delicious REAL Sourdough Banana Bread!