Preheat your oven to 350°F (175°C). Grease a muffin tin or line it with paper liners.
In a large bowl, mash the ripe bananas until smooth.
Whisk in the melted butter.
Stir in the egg and vanilla extract.
Add the sugar and mix well.
In another bowl, combine the flour, baking soda, and salt.
Gradually add the dry ingredients to the banana mixture.
Gently fold in the blueberries.
Divide the batter evenly among the muffin cups.
Bake for 20-25 minutes or until golden brown.
Allow to cool for a few minutes before serving.