Preheat your oven to 350°F (175°C) and grease a 9-inch loaf pan lightly with butter or oil to prevent sticking.

In a large mixing bowl, combine the melted unsalted butter with both brown and granulated sugars, whisking until smooth and creamy.

Mash ripe bananas directly into your wet mixture until mostly smooth, ensuring their natural sweetness and moisture are fully incorporated.

Sprinkle the all-purpose flour, baking soda, baking powder, salt, and ground cinnamon evenly over the wet mixture and gently fold until just combined.

Pour the batter into the prepared loaf pan, smoothing the top with a spatula.

Place your pan in the preheated oven and bake for 45 to 55 minutes, checking for doneness with a toothpick.

Allow to cool in the pan for 10 to 15 minutes, then transfer to a wire rack to cool completely.