Preheat your oven to 425F (220C) and line a 12-count muffin tin with liners. Set aside.

In a large mixing bowl, combine mashed bananas, melted butter, and sugars and stir well.

Add buttermilk, egg, and vanilla extract and stir until well incorporated.

In a separate, medium-sized mixing bowl, whisk together flour, baking powder, baking soda, and salt.

Add the dry mixture to the wet and use a spatula to gently fold ingredients together until about 50% combined.

Add chocolate chips and fold into the batter until batter is just combined and chips are well distributed.

Evenly divide batter into prepared muffin tin. Top with additional chocolate chips and a light sprinkling of granulated sugar, if desired.

Place in center rack of 425F (220C) preheated oven. Bake for 8 minutes then, without opening oven door, reduce oven temperature to 350F (175C) and continue to bake another 7-8 minutes, until baked through and a toothpick inserted in the center comes out clean or with a few moist crumbs.

Allow muffins to cool in pan for 5-10 minutes then carefully transfer to a cooling rack to cool completely before enjoying (I use a butter knife to gently lift them out of the pan and then pick them up carefully and transfer them).