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

In a large mixing bowl, combine 3 mashed ripe bananas with 1/2 cup of melted unsalted butter. Stir in 1 cup of granulated sugar, 1 beaten egg, and 1 teaspoon of vanilla extract until well combined.

In another bowl, whisk together 1 1/2 cups of all-purpose flour, 1 teaspoon of baking soda, and 1/2 teaspoon of salt. Gradually add this dry mixture to your banana mixture, folding gently.

Mix 2 teaspoons of ground cinnamon and 1/4 cup of brown sugar in a small bowl for the cinnamon swirl mixture.

Pour half of your banana batter into the prepared loaf pan, sprinkle half of the cinnamon-sugar mixture, then add the remaining batter and top with the rest of the cinnamon-sugar blend.

Using a butter knife, gently swirl the cinnamon-sugar mixture through the banana batter.

Bake for 60-70 minutes, or until a toothpick inserted comes out clean. If it browns too quickly, tent it with aluminum foil.

Allow to cool in the pan for about 10 minutes, then remove and let cool completely on a wire rack before slicing.