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 until smooth. Add sugar, eggs, and vanilla; mix until fully incorporated.
03 - In a separate bowl, sift together flour, baking soda, and salt.
04 - Add dry ingredients to wet ingredients and mix just until combined. Avoid overmixing to prevent tough texture.
05 - In a small bowl, mix together granulated sugar and ground cinnamon until well blended.
06 - Pour half the batter into prepared pan. Sprinkle with half the cinnamon sugar mixture. Add remaining batter, then top with remaining cinnamon sugar.
07 - Gently run a knife through the batter to swirl the cinnamon sugar layers, creating a marbled pattern.
08 - Bake for 50–60 minutes until a toothpick inserted in the center comes out clean.
09 - Let bread cool in pan for 10 minutes, then transfer to wire rack to cool completely before slicing.