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