1. The day before you want banana bread, mix together sourdough starter, melted butter or olive oil, eggs, and flour. Cover well and allow to ferment at room temperature for 6-8 hours. You can also start this at night right before you go to bed.
2. After the dough has sat at room temperature (it should be lighter and fluffier now), put it in the fridge and allow it to ferment for another 12-20 hours.
3. The next day, preheat oven to 350 degrees.
4. Using a stand mixer with the paddle attachment, or an electric whisk, add mashed bananas, brown sugar, vanilla, salt, cinnamon and nutmeg to a mixing bowl.
5. Set on low to medium speed and mix until everything is completely combined. The pre-fermented dough takes a little extra time to be fully incorporated. Once things are mostly incorporated, sprinkle the baking powder and baking soda on top of the batter, and then mix it in until evenly combined, but try not to over-mix.
6. Butter a loaf pan and then pour batter into pan.
7. Bake for 50-60 minutes.
8. Allow to cool in the pan for one hour before removing and eating. Don’t skip this step! After cooled, enjoy with butter and flaky salt:).
