Preheat your oven to 350°F (175°C). Line your muffin tin with liners.
In a bowl, mash the ripe bananas with a fork or potato masher until smooth.
Add the melted butter into the mashed bananas, stirring until well combined. Add the beaten egg and vanilla extract, mixing thoroughly.
In a separate bowl, mix the sugar, baking soda, salt, and flour.
Combine the wet and dry mixtures, stirring until just incorporated. Avoid overmixing to maintain the muffins' texture.
Spoon the batter into the prepared muffin cups, filling each about two-thirds full.
Bake in the preheated oven for approximately 20-25 minutes or until a toothpick inserted into the center comes out clean.
Allow the banana muffins to cool in the tin for a few minutes before transferring them to a cooling rack. Serve and enjoy!