Preheat the oven to 350 degrees. Line two 12 cup muffin pans with 18 liners. I like to spread them out and do 8 and 7 in each pan.
In a large mixing bowl, combine the melted butter, brown sugar, and white sugar. Whisk together until smooth, creamy, and no brown sugar lumps remain.
Whisk in the sour cream, then add the eggs, one at a time, whisking well after each addition. Stir in the vanilla.
In another bowl, mash the bananas then whisk them into the sour cream mixture.
Sprinkle the flour, baking soda, baking powder, salt, and cinnamon on top of the wet ingredients and give them a little whisk. Then use a spatula to gently fold everything together until no white remains. Stir in the chocolate chips, if desired.
Scoop the batter into the prepared liners. Bake for 20-25 minutes, or until the tops of the muffins are set and spring back when touched. Cool for a few minutes in the pans, then remove the cupcakes to a cooling rack to cool completely