Preheat your oven to 375°F (190°C) and prepare a muffin pan by lining it with paper liners.

In a large mixing bowl, mash the overripe bananas until smooth with minimal lumps.

Mix in the beaten egg, cooled melted butter, and vanilla extract until well combined.

In a separate bowl, whisk together the all-purpose flour, brown sugar, baking soda, and salt.

Gently fold the dry ingredients into the wet mixture until just combined, being careful not to overmix.

Fold in any optional add-ins like chocolate chips or chopped walnuts if desired.

Fill each muffin liner about 3/4 full with the batter using a spoon or cookie scoop.

Bake in the preheated oven for 15 to 21 minutes, performing the toothpick test for doneness.

Cool the muffins in the pan for 5 minutes before transferring them to a wire rack to cool completely.