Adjust oven rack to lower middle position and preheat oven to 350°. Generously Butter a 9-inch loaf pan; flour the pan, shake out excess flour and set aside.
Sift the flour, baking soda and salt onto a sheet of waxed paper; set aside.
In a medium bowl, Mix together mashed bananas, chopped walnuts, yogurt and vanilla; set aside.
In a large bowl, combine sugar and eggs and whisk until smooth. Whisk the warm butter slowly into the egg mixture
Using a rubber spatula, alternately fold the sifted flour mixture and the banana mixture into the egg mixture until just combined, and batter still looks a little chunky - don't over mix. Scrape batter into prepared loaf pan.
Bake until loaf is proud and golden brown and a toothpick inserted in center comes out clean, 45-55 minutes. Allow pan to cool for 10 minutes, then invert onto a wire rack.