Preheat your oven to 350°F (175°C).

In a large mixing bowl, combine melted butter, brown sugar, and granulated sugar. Whisk until smooth. Add sour cream, eggs, vanilla extract, and mashed bananas, mixing well.

Sprinkle flour, baking soda, baking powder, salt, and cinnamon over the wet mixture, and fold gently until just combined.

Prepare your loaf pan by greasing it well.

Pour the batter into the prepared loaf pan, filling it about two-thirds full.

Bake in the preheated oven for 45-55 minutes, until a toothpick comes out with a few moist crumbs.

Let the bread cool in the pan for 10-15 minutes before transferring it to a wire rack.