Preheat your oven to 350°F (175°C). Grease a metal 9x5-inch loaf pan with butter or nonstick spray, making sure to get into the corners. Set it on a sturdy baking sheet so it’s easy to move in and out of the oven.

In a large mixing bowl, mash the ripe bananas with a fork until mostly smooth but with a few soft pieces still visible.

Pour the ½ cup melted butter over the mashed bananas and stir until combined. Add the ¾ cup granulated sugar and ¼ cup brown sugar, and mix until the mixture looks thick and glossy.

Beat in the eggs, one at a time, stirring well after each addition. Add the vanilla extract and stir again.

In a separate bowl, whisk together the flour, 1 ½ teaspoons cinnamon, baking powder, baking soda, and salt.

Gently add the dry ingredients to the wet banana mixture in two additions, stirring just until the flour disappears each time.

In a small bowl, make the cinnamon swirl topping by stirring together 2 tablespoons sugar, 1 teaspoon cinnamon, and 1 tablespoon melted butter until it looks like damp, sandy crumbs.

Spoon about half of the banana batter into the prepared loaf pan in uneven scoops, letting it mound up a little here and there. Sprinkle half of the cinnamon topping over this first layer.

Spoon the remaining batter on top in big dollops, letting some spots be a bit higher than others. Sprinkle the rest of the cinnamon topping over the top.

Using the tip of a butter knife, gently drag it through the batter in a few loose swirls.

Place the pan (on its baking sheet) into the preheated oven and bake for 55–65 minutes, or until the top is deep golden.

Let the loaf cool in the pan on a wire rack for at least 15–20 minutes. Run a knife around the edges, then carefully lift or tip the loaf out of the pan.