Preheat the oven to 350°F (175°C). Grease a standard loaf pan or line it with parchment paper.
Mash the two ripe bananas in a large mixing bowl.
Stir in the melted butter, brown sugar, egg, and vanilla extract until combined.
Add the flour, baking soda, cinnamon, and salt.
Stir gently until the ingredients are just combined. Do not overmix.
Fold in walnuts or chocolate chips if using.
Pour the batter into the prepared loaf pan and spread evenly.
Bake for 45–55 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.
Cool in the pan for 10–15 minutes, then transfer to a wire rack.
Slice and serve warm or at room temperature.