Preheat the oven to 350°F (175°C) and grease a 9x5-inch loaf pan.
Mash the bananas in a large bowl, then stir in the melted butter.
Whisk in the sugar, beaten egg, and vanilla extract.
Sprinkle the baking soda and salt over the mixture and stir in.
Add the flour and stir just until combined, being careful not to overmix.
Pour the batter into the prepared loaf pan.
Bake for 50-55 minutes, until a toothpick inserted in the center comes out clean.
Cool in the pan for 10 minutes, then transfer to a cooling rack.