Step 1: Preheat your oven to 350°F (175°C) and grease a 9x5 inch loaf pan with butter or non-stick spray.
Step 2: In a large bowl, mash the overripe bananas until they are smooth with only minor lumps.
Step 3: Stir the melted butter into the mashed bananas until well combined.
Step 4: Mix in the sugar, beaten egg, and vanilla extract until the mixture is uniform.
Step 5: Sprinkle the baking soda and salt over the mixture and stir them in gently.
Step 6: Add the flour and fold it in using a spatula just until the flour disappears; do not overmix.
Step 7: Pour the batter into the prepared pan and bake for 50-60 minutes, or until a tester comes out clean.
Step 8: Let the bread cool in the pan for 10 minutes before moving it to a wire rack to cool completely.