In a large bowl, mix together sourdough starter, honey, melted butter, and flour.
Cover and allow to ferment at room temperature for 12-24 hours (optional).
After the muffin batter has fermented, preheat the oven to 350, line or grease the muffin tins.
To the batter, add mashed banana, eggs, vanilla, salt, baking soda and baking powder.
Using the paddle attachment on the stand mixer, mix together ingredients on low to medium speed until everything is combined well.
Pour into muffin tins and bake for 20-25 minutes, or until they start to turn golden brown. They are done when a toothpick or knife inserted into the middle of the muffin comes out clean.
Notes
If you are new to sourdough you can find how to make a super easy and no fail sourdough starter here.
The dough will be really thick after fermentation. This is totally normal.
Sourdough can be fickle. Your outcome may depend on how hydrated your starter is.
The batter will not look like it has risen at all after fermentation. This is totally normal.