Preheat your oven to 350°F (175°C) and grease a 9x5 inch loaf pan.
In a large mixing bowl, combine the mashed bananas and melted butter. Mix until well blended.
Stir in the baking soda and salt. Then, add the sugar, beaten egg, and vanilla extract, mixing well.
Sprinkle in 1 teaspoon of cinnamon, then gradually add the flour while mixing until just combined (don't overmix!).
In a separate small bowl, prepare the cinnamon swirl by combining brown sugar and 1 teaspoon of cinnamon.
Pour half of the banana bread batter into the prepared loaf pan. Sprinkle half of the cinnamon sugar mixture over the batter.
Pour the remaining batter on top and sprinkle the rest of the cinnamon sugar mixture over it. Use a knife or toothpick to gently swirl the layers together in a figure-eight motion.
Bake in the preheated oven for 60-65 minutes or until a toothpick inserted into the center comes out clean.
Allow the bread to cool in the pan for about 10 minutes, then transfer it to a wire rack to cool completely.
Notes
Slice the banana bread and arrange it on a decorative platter, dusting the top lightly with powdered sugar for an elegant touch. Serve with butter or cream cheese for an indulgent treat.