Preheat your oven to 350°F (175°C). Grease a 4×8-inch loaf pan and line with parchment if you like for easy removal.

In a medium bowl, mash the ripe bananas with a fork until mostly smooth. Stir in the melted butter until blended.

Add the baking soda and a pinch of salt. Mix in the granulated sugar, beaten egg, and vanilla until combined.

Sprinkle in the flour and fold gently with a spatula. Stop when you no longer see dry streaks; do not overmix.

In a small bowl, combine the ground cinnamon and brown sugar for the swirl.

Pour half the banana batter into the prepared pan and smooth the top lightly.

Evenly sprinkle half of the cinnamon-sugar mixture over that layer.

Add the remaining batter on top and spread gently. Sprinkle the remaining cinnamon-sugar across the surface.

Use a knife or skewer to swirl the cinnamon mix through the top layer in a few figure-eights — don’t overdo it or the swirl will disappear.

Bake for 50 to 60 minutes. Start checking at 50 minutes; a toothpick inserted in the center should come out clean or with a few moist crumbs.

If the top browns too fast, tent loosely with foil.

Let the bread cool in the pan for 10 minutes, then lift out with the parchment (if used) and transfer to a wire rack to cool completely before slicing.