Grease a 9x5 pan with vegetable spray. Also preheat your oven to 350 degrees Fahrenheit.

In the bowl of your mixer cream together the butter and dark brown sugar.

While the butter is creaming sift together the flour, baking soda and salt. I like to sift the ingredients onto a piece of parchment or foil. That way you can easily funnel the ingredients into the mixing bowl. Once you have the dry ingredients sifted, mash the four bananas into a small bowl.

Once the butter and dark brown sugar are creamed together, turn the mixer to low and add the eggs one at a time. Make sure to fully incorporate the first egg before adding the second.

Then add the bananas to the mixture.

Once the bananas are fully incorporated, slowly add the dry ingredients. If you sift the ingredients onto a piece of parchment or foil your job will be a lot easier.

Once everything is incorporated, remove the mixing paddle and add the walnuts. Mix them in by hand. Once incorporated, pour the batter into the prepared loaf pan.

Place the loaf pan in the center of a preheated oven and bake for 1 hour, or until fully cooked. To check for doneness, insert a skewer into the center of the bread. When the skewer comes out cleanly, the loaf is fully cooked.

Remove the loaf from the oven and let cool in the pan for at least 5 minutes. After the bread has slightly cooled, remove it from the pan and let it fully cool on a wire rack.