Preheat your oven to 350°F (175°C) and grease a 9-inch loaf pan.

Combine melted butter with brown and white sugar. Mix until smooth (2-3 minutes).

Stir in the sour cream, then add eggs one by one, also adding vanilla extract.

Mash bananas in a separate bowl, then fold into the batter.

In a separate bowl, whisk together flour, baking soda, baking powder, salt, and cinnamon. Gradually add to batter.

Pour batter into prepared loaf pan and bake for 45-55 minutes, checking with a toothpick for doneness.

Cool in the pan for 15 minutes, then transfer to a wire rack to cool completely.