Preheat the Oven: Preheat your oven to 350°F (175°C). Grease a 9×5-inch loaf pan and line it with parchment paper for easy removal.

Prepare the Batter:

• In a large mixing bowl, combine the mashed bananas, melted butter, granulated sugar, and brown sugar. Mix until smooth.
• Add the eggs one at a time, followed by the vanilla extract, and whisk until fully incorporated.
• In a separate bowl, whisk together the flour, baking soda, and salt. Gradually fold the dry ingredients into the wet mixture until just combined. Avoid overmixing.

Make the Cinnamon Swirl:

• In a small bowl, mix the granulated sugar and cinnamon. Set aside.

Assemble the Loaf:

• Pour half of the banana bread batter into the prepared loaf pan and spread evenly.
• Sprinkle half of the cinnamon-sugar mixture over the batter, then dot with half of the softened butter. Use a knife to gently swirl the mixture into the batter.
• Add the remaining batter, sprinkle with the rest of the cinnamon-sugar mixture, and dot with the remaining butter. Swirl again lightly to create a marbled effect.

Bake: Place the loaf pan in the preheated oven and bake for 50–60 minutes, or until a toothpick inserted into the center comes out clean.

Cool and Serve: Allow the banana bread to cool in the pan for 10 minutes before transferring it to a wire rack to cool completely. Slice and enjoy!