Preheat your oven to 350°F (175°C) and grease a 9-inch bread pan or line it with parchment paper.

In a large mixing bowl, whisk together the melted unsalted butter, brown sugar, and white sugar until smooth.

Add the sour cream, mixing until fully blended, then stir in the eggs one at a time, and finally add the vanilla extract.

Mash the very ripe bananas in a separate bowl, then fold them into the wet mixture.

Sift together the flour, baking soda, baking powder, salt, and ground cinnamon. Gradually mix this into the wet ingredients until just combined.

Pour the batter into the prepared bread pan and smooth the top with a spatula. Bake for 45-55 minutes.

Once baked, cool the bread in the pan for 15 minutes before transferring to a wire rack.