Preheat oven to 350°F (175°C). Grease a 9x5-inch loaf pan.

In a large bowl, mash the bananas and stir in melted butter until smooth.

Mix in sugar, egg, and vanilla extract.

Add baking soda and salt; stir to combine.

Fold in flour just until mixed—do not overmix.

Pour batter into the prepared loaf pan and smooth the top.

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

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