Preheat the oven to 375°F Lightly butter of spray the bottom and sides of a 9 inch loaf pan.
place the butter and sugar in a large mixing bowl and beat with an electric mixer on low speed for 1 minute or until the sugar is completely mixed into the butter. Add the eggs and mix for 1 minute, or until the batter is smooth. Add the bananas and mix for 1 minute or until no large chunks remain. The batter will be lumpy but the pieces of banana should all be 1/2 inch or smaller.
Add the baking soda and salt and mix on low speed for 1 minute or until combined. Add the flour and mix on low speed for 1 minute, scraping the sides of the bowl occasionally, until all of the flour is incorporated.
Stir in walnuts. (optional).
Pour the batter into the loaf pan and bake for 15 minutes. Reduce the oven heat to 350 F and bake for 45 minutes or until a toothpick inserted in the center of the loaf comes out clean.
Remove the bread from the pan and place it on a cooling rack. (If you let the bread cool in the pan the bottom will become soggy.).