Preheat the oven to 375 F and prepare a muffin tin with cups or spray. (I use paper muffin cups)
Peel and mash your bananas in a small bowl. Assemble the dry ingredients in another small bowl and mix.
In a larger bowl combine the melted butter and sugar until smooth. Add in the miso, egg and bananas. It will look split but do not worry. Add in the dry ingredients and stop mixing as soon as the larger streaks of flour are incorporated. I’m serious, don’t overmix this.
Fill the muffin cups evenly, break up the topping into small bits on top of each muffin and sprinkle with some finishing salt if you’re feeling extra. Pop that in the oven for 20 - 22 minutes or until the tester comes out cleanish.