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

In a large mixing bowl, mash the ripe bananas with a fork or potato masher until smooth with some small lumps.

Add the melted butter to the mashed bananas and stir until well combined.

In a separate bowl, combine the baking soda and salt with the all-purpose flour.

Add the sugar, beaten egg, and vanilla extract to the banana mixture and stir until fully incorporated.

Gradually add the flour mixture to the wet ingredients and mix gently until just combined.

In a small bowl, mix together the ground cinnamon and brown sugar.

Pour half of the banana bread batter into the prepared loaf pan, sprinkle half of the cinnamon-brown sugar mixture over it, then pour the remaining batter on top and finish with the rest of the cinnamon-brown sugar mixture. Gently swirl the mixture into the batter.

Bake in the preheated oven for 60-65 minutes, checking for doneness with a toothpick.

Allow the bread to cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.