Preheat your oven to 350°F (175°C) and grease a 9x5-inch loaf pan.
In a large mixing bowl, mash the ripe bananas with a fork until smooth.
Add the melted butter and sugar to the bananas and whisk until combined.
Beat in the eggs and vanilla extract until the mixture is smooth.
Sprinkle the baking soda and salt over the mixture and stir to incorporate.
Gently fold in the flour using a spatula; do not overmix (batter will be thick).
(Optional) Fold in the sour cream/yogurt for extra moisture.
Pour the batter evenly into the prepared loaf pan.
Bake for 50-55 minutes, or until a toothpick inserted in the center comes out clean.
Let cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.