Preheat oven to 180C/350F and grease a 6hole muffin tin with butter.
Mash bananas in a bowl. You want it to be fairly squishy - but a few chunks is fine.
Mix the sourdough starter, 2 eggs, vanilla extract and oil in a bowl. Whisk together until well combined. It's ok if the oil sits on the top, it will combine once it is poured into the dry ingredients.
Stir the mashed banana through the liquid ingredients.
In a separate bowl mix together all purpose flour, salt, cinnamon, nutmeg, baking powder, baking soda and sugars.
Now pour the liquid ingredient mixture into the dry ingredients. Gently fold together until just mixed - don't over mix or the muffins will be tough.
Spoon mixture into greased muffin tin. This recipe will fill a 6 hole muffin (each hole around ¾ full). Sprinkle each muffin with a little raw sugar (this is optional).
Bake at 180C/350F for approximately 25 to 30 minutes or until muffins are golden brown. Remember your oven might run hotter or cooler than mine, so use your discretion.