This sour cream banana bread with a cinnamon swirl tastes like a combination of coffee cake and banana bread. For the best flavor, use very overripe bananas.
Preheat oven to 350℉. Grease a 9x5-inch loaf pan and line with parchment paper.
Prepare the cinnamon swirl: In a small bowl, whisk together sugar and cinnamon. Set aside.
Prepare the batter: Mash the bananas in a large bowl with a whisk or fork until almost smooth. Add sugar and eggs. Stir to combine. Add the melted butter, sour cream, and vanilla. Mix until smooth. Add the flour, baking powder, and salt. Mix until a thick batter forms.
Spread ⅓ of the batter into the prepared pan. Top with about ⅓ of the cinnamon sugar mixture. Repeat with the remaining batter and cinnamon sugar. Finish with the cinnamon-sugar.