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.
Stir in the melted butter until well combined.
Add baking soda and salt, and mix well.
Stir in the sugar, beaten egg, and vanilla extract.
Gradually mix in the flour until just combined; do not overmix.
Fold in the chopped nuts gently.
Divide the batter evenly among the muffin cups, filling each about 2/3 full.
Bake for 20-25 minutes or until a toothpick inserted into the center comes out clean.
Let the muffins cool in the tin for a few minutes before transferring to a wire rack.