Prepare the Oven and Muffin Tin:
Preheat your oven to 350°F (175°C). Line a muffin tin with paper liners or grease it with nonstick spray.
Mix the Dry Ingredients:
In a medium bowl, whisk together the flour, baking soda, baking powder, and salt. Set aside.
Combine the Wet Ingredients:
In a large bowl, mash the bananas until smooth. Stir in the melted butter, granulated sugar, brown sugar, egg, and vanilla extract until well combined.
Incorporate the Dry Ingredients:
Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix; the batter should be slightly lumpy.
Fold in the Nuts:
Gently fold in the chopped nuts.
Fill the Muffin Tin:
Spoon the batter into the prepared muffin tin, filling each cup about ¾ full. Sprinkle extra nuts on top for added crunch.
Bake:
Bake in the preheated oven for 18-22 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Cool:
Remove the muffins from the oven and let them cool in the tin for 5 minutes. Transfer to a wire rack to cool completely.