01 - Preheat oven to 350°F. Grease and flour a 9 x 5 inch loaf pan or line with parchment paper.
02 - In a large bowl, whisk mashed bananas and melted butter. Add sugar, eggs, and vanilla; mix until smooth.
03 - In a separate bowl, sift flour, baking soda, and salt. Add dry ingredients to wet mixture and mix just until combined—avoid overmixing.
04 - In a small bowl, combine granulated sugar and ground cinnamon for the swirl mixture.
05 - Pour half the batter into prepared pan. Sprinkle half the cinnamon sugar evenly over batter. Add remaining batter, then top with remaining cinnamon sugar mixture. Use a knife to gently swirl creating a marbled effect.
06 - Bake for 50-60 minutes until a toothpick inserted in center comes out clean.
07 - Let bread cool in pan for 10 minutes, then transfer to wire rack to cool completely.