In a bowl add the ripe bananas and use a fork to mash the bananas down. To the mashed bananas add the sour cream, melted butter, sugars, vanilla extract, and ¼ cup (2oz) of the peanut butter to the bananas. Whisk until combined.
Pour half of the batter into the prepared pan, then spoon half of the remaining peanut butter in blobs on top of the batter and use a knife to swirl it. Top with remaining batter and repeat.