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 together mashed bananas and melted butter. Add sugar, eggs, and vanilla; mix until smooth.
03 - In another bowl, sift together flour, baking soda, and salt. Add dry ingredients to wet ingredients and mix just until combined.
04 - In a small bowl, mix together the cinnamon and sugar for the swirl.
05 - Pour half the batter into prepared pan. Sprinkle half cinnamon sugar over batter. Top with remaining batter, then remaining cinnamon sugar.
06 - Use a knife to gently swirl the cinnamon sugar through the batter, creating a marbled effect.
07 - Bake for 50-60 minutes, or until a toothpick inserted in center comes out clean.
08 - Allow bread to cool in pan for 10 minutes before transferring to wire rack to cool completely.