**Preheat the oven**
Preheat your oven to 350°F (175°C). Line a muffin tin with paper liners or lightly grease with nonstick spray.
**Mash the bananas**
In a large mixing bowl, mash the ripe bananas until smooth.
**Mix the wet ingredients**
Stir in the melted butter, brown sugar, egg, and vanilla extract until well combined.
**Combine the dry ingredients**
In a separate bowl, whisk together the flour, baking soda, baking powder, and salt.
**Mix the batter**
Gradually fold the dry ingredients into the wet ingredients, mixing just until combined. Be careful not to overmix. If using chocolate chips or nuts, fold them in at this stage.
**Fill the muffin tin**
Divide the batter evenly among the muffin cups, filling each about 3/4 full.
**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 and serve**
Let the muffins cool in the tin for 5 minutes before transferring to a wire rack to cool completely. Enjoy warm or at room temperature.