Preheat your oven to 350°F (175°C) and grease a muffin tin or line it with paper liners.
In a large bowl, mash the bananas until smooth.
Mix in the melted butter, both sugars, and the egg until well combined.
In another bowl, whisk together the flour, baking soda, and salt.
Gradually fold the dry ingredients into the wet mixture until just combined; avoid overmixing.
Spoon the batter into the prepared muffin tin and bake for 18-22 minutes, or until golden brown and a toothpick inserted in the center comes out clean.
Allow to cool slightly before serving.
