Preheat oven to 350 degrees. Mash bananas in a mixing bowl. With a wooden spoon, mix butter into mashed bananas. Mix in the sugar, egg and vanilla. Sprinkle the baking soda and salt over the mixture and mix in. Add the flour, mixing well. Then add nuts and stir well. Pour mixture into a greased 4 x 8 inch loaf pan sprayed with cooking oil, and lined with parchment paper. Bake for 1 hour, test with toothpick. Cool on a rack 10-15 minutes. Remove from pan. I wrap in plastic wrap and then foil. Store in refrigerator, or freeze.