Preheat your oven to 350°F (175°C) and grease a 9x5 inch loaf pan.
In a large mixing bowl, combine the mashed bananas with the melted butter. Mix well to create a smooth paste.
Stir in the baking soda and salt. Then, add the sugar, beaten egg, and vanilla extract, mixing until combined.
Gradually add the all-purpose flour, carefully folding it into the mixture until just combined (do not over-mix).
In a small bowl, mix the ground cinnamon and brown sugar together to create your cinnamon swirl mixture.
Pour half of the banana batter into the prepared loaf pan, then sprinkle half of the cinnamon-brown sugar mixture over it.
Pour the remaining batter on top and finish with the rest of the cinnamon-brown sugar mixture, gently swirling it into the batter using a knife or skewer 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.
Allow the banana bread to cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.
Notes
Slice the banana bread and serve warm with a pat of butter on top, or enjoy it with a dollop of cream cheese spread for extra creaminess. Garnish with a sprinkle of cinnamon for a beautiful finish!