Heat oven to 350°. Grease a loaf pan with butter and dust with flour; set aside.
In a large bowl, combine dry ingredients: flour, baking soda, sugar, and salt.
In separate bowl, combine, butter, milk, sour cream, vanilla, egg, egg yolk, peanut butter, homemade Nutella (or store-bought), and bananas. Mix until smooth. Scoop dry ingredients into wet, about 1/2 cut at a time, until all ingredients are mixed together.
Pour batter into prepared loaf pan and bake until golden brown, about 40-45 minutes. Let cool for at least 10 minutes before slicing and serving.