Preheat your oven to 350°F (175°C) and grease a 9x5-inch loaf pan.

In a mixing bowl, mash the ripe bananas with a fork until smooth.

Stir in the melted butter until well combined.

Mix in the baking soda and salt.

Add the sugar, beaten egg, and vanilla extract, stirring until the mixture is smooth.

Gradually add the all-purpose flour to the banana mixture, stirring until just combined. Be careful not to overmix!

In a separate small bowl, combine the ground cinnamon and brown sugar to create the cinnamon swirl mixture.

Pour half of the banana bread batter into the prepared loaf pan and spread it evenly.

Sprinkle half of the cinnamon swirl mixture over the batter in the pan.

Pour the remaining banana batter on top, spreading it gently.

Lastly, sprinkle the remaining cinnamon swirl mixture evenly over the top of the batter.

Using a knife or a skewer, gently swirl the batter to create a marbled effect.

Bake in the preheated oven for 60-65 minutes, or until a toothpick inserted into the center comes out clean.

Remove from the oven and allow the bread to cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.