Preheat your oven to 350°F (175°C).

Line your muffin tin with paper liners or grease it with butter.

In a mixing bowl, mash the ripe bananas with a fork until smooth.

Add melted butter, sugar, beaten egg, and vanilla extract to the mashed bananas and stir until well combined.

In a separate bowl, whisk together flour, baking soda, and salt.

Gently fold the dry ingredients into the wet mixture until just combined.

If using nuts or chocolate chips, fold them into the batter.

Spoon the batter into the prepared muffin tins, filling each cup about 2/3 full.

Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted into the center comes out clean.

Remove the muffins from the oven and let them cool in the tin for 5 minutes before transferring to a cooling rack.