Preheat oven to 350F°. Grease a loaf pan and set aside.
If you have a helper, put him or her to work mashing your bananas.
In a large bowl or stand mixer, cream butter and sugar. Add in eggs, beat well. Add in your dry ingredients. Scrape the sides of your bowl often. Mix in half of the mashed bananas. When your mixture is combined well, add in the remaining bananas. If adding in walnuts, chop to your desired size. I went for a super small chopped size by using my food processor. It's the easiest and most consistent method. You may toss them into your mixture now or mix in by hand.
Your batter will appear extremely wet and sloppy. I was fearful that it was so moist the bread wouldn't turn out. So fear not when you see how goopy it is. Your bread will turn out.
Pour batter into loaf pan. Bake for 60-70 minutes. Check at the 30-40 minute mark. If the top of your loaf is darkening, make a foil hat for your loaf. Take a foot long piece of foil and fold in half, place this ontop of your loaf. It will allow air to circulate while protecting the crust from browning further. At the 60 minute mark, check for doneness by using a toothpick. It is ready to be removed from the oven when only a few moist crumbs stick to your toothpick. You don't want wet batter coming out. If it is still too wet, cook for an additional 10 minutes and recheck.
Let cool in pan for 5-10 minutes. Then carefully transfer to a cooling rack. Continue cooling for 20 or more minutes before slicing into. And as you should always do with bread, use a serrated knife to slice.