Preheat oven to 350 degrees F. and sprayÂ 2 bread pans(9x4 or 9x5 inch) with cooking spray.
Cream butter and sugar into a large bowl until light and fluffy. Add eggs, sour cream and vanilla mixing to combine. Mash all bananas and add to bowl, mixing to combine. Add flour, cocoa, baking soda, baking powder, salt and marshmallow bits, stirring to combine.
Divide between the 2 prepared bread pans, spreading evenly on top. Bake for 55-60 minutes or until baked through. Remove and let cool for 20 minutes before removing from pan. When cool, cut into slices and serve.
If you want the bread to be dense and almost bread pudding like leave out the baking soda and baking powder and reduce the flour to 1 cup. For a more traditional textured bread pudding follow the recipe as stated :)