Preheat your oven to 350°F (175°C) and line a muffin tin with paper liners.
In a mixing bowl, mash the ripe bananas with a fork until smooth.
Add melted butter to the mashed bananas and mix well.
Stir in baking soda and salt.
Add sugar, beaten egg, and vanilla extract, then mix until combined.
Gradually add the all-purpose flour, stirring until just incorporated.
If desired, fold in nuts or chocolate chips.
Divide the batter evenly among the muffin cups, filling each about 2/3 full.
Bake in the preheated oven for 18-20 minutes, or until a toothpick comes out clean.
Allow muffins to cool in the pan for a few minutes before transferring to a wire rack.