Mash bananas until mostly smooth, with a few small lumps left behind.
Add the melted butter to the mashed bananas and stir until combined. Mix in the sugar, egg, and vanilla.
Sprinkle the baking soda and salt over the mixture and stir gently. Finally, fold in the flour just until no dry streaks remain. Stop as soon as the batter comes together.
Add the chopped nuts and fold them in lightly. They should be evenly distributed but not crushed into the batter.
Grease a standard loaf pan or line it with parchment paper. Pour the batter in and smooth the top gently. Don’t tap the pan aggressively; banana bread bakes best when the air stays inside.
Bake at 350°F (175°C) for 50–60 minutes.
Start checking at 50 minutes. A toothpick inserted into the center should come out mostly clean, with a few moist crumbs.
