Preheat the oven to 350°F (175°C). Grease a 4x8 inch loaf pan well, or line it with parchment for easy removal.

In a mixing bowl, mash the overripe bananas with a fork until mostly smooth; small lumps are okay.

Stir the melted butter into the mashed bananas until the mixture is even.

Sprinkle in the baking soda and add a pinch of salt; mix briefly so they combine.

Add the sugar, beaten egg, and vanilla extract. Stir until blended and glossy.

Gently fold in the flour until just incorporated — overmixing will make the loaf dense. If using walnuts, fold them in now.

Pour the batter into the prepared loaf pan and smooth the top with a spatula.

Bake for 60–65 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs. If the top browns too quickly, loosely tent with foil for the last 15 minutes.

Let the bread cool in the pan for 5–10 minutes, then transfer to a wire rack to cool completely before slicing.