Preheat the oven to 350°F and line or grease a loaf pan. Bring a large pot of water to a boil.
Peel the bananas and roughly chop the peels. Simmer the peels in boiling water for 5 minutes and then drain, rinse under cold water, and set aside.
Using a hand mixer or a stand mixer fitted with the paddle attachment, mix the butter and sugar together until incorporated, light, and fluffy.
In a medium-size bowl, mix the flour with the baking soda, baking powder, and salt.
Using a blender or food processor, blend the bananas, peels, eggs, buttermilk, and vanilla.
Slowly beat the banana mixture into the butter mixture until incorporated. Beat in the flour mixture until combined. Stir in any optional add-ins and evenly spread with the crumble if using.
Pour the mixture into the prepared pan and bake for about 1 hour or until a toothpick comes out clean.