Preheat oven to 350°F (175°C).

Grease a 9x5-inch loaf pan or line it with parchment paper.

In a large bowl, mash the bananas with a fork until smooth.

Stir in the melted butter until well combined.

Add sugar, beaten egg, and vanilla extract. Mix until everything is evenly blended.

Sprinkle baking soda and salt over the mixture and stir gently.

Add the flour and stir just until the flour disappears—do not overmix.

Pour the batter into the prepared loaf pan and spread it evenly.

Bake for 50 to 60 minutes, or until a toothpick inserted into the center comes out clean.

Let the banana bread cool in the pan for 10 minutes.

Transfer to a wire rack to cool completely before slicing.