01 -
Preheat oven to 175°C (350°F). Lightly grease and flour a 23×13-cm (9×5-inch) loaf pan or line with parchment paper. Set aside.
02 -
In a large bowl, melt the butter and let cool slightly. Whisk in the sugar, then add eggs and vanilla. Stir in the flour and baking soda. Fold in the mashed bananas until just combined.
03 -
In a small bowl, use a fork to stir together the melted butter, granulated sugar, brown sugar, and cinnamon until thick and well combined. If mixture is too thick to swirl, add an additional tablespoon of melted butter until it reaches the right consistency.
04 -
Spread 1/4 of the batter evenly into the bottom of the prepared pan. Dollop 1/4 of the cinnamon sugar mixture over the batter and make a thick swirl through the batter with a table knife or wooden spoon. Add another 1/4 of the batter, then dollop and swirl more cinnamon mixture. Repeat with remaining batter and cinnamon mixture, making large swirls throughout the top layer.
05 -
Place loaf pan on a baking sheet and bake for 65-70 minutes or until golden brown and a toothpick inserted in the center comes out clean. Let the bread cool in the pan for at least 30 minutes before removing to a wire rack to cool completely.