Preheat oven to 350, line the bottom of a spring form pan with parchment paper and then spray with cooking spray and set aside.
In a microwave safe bowl microwave butter for 30 seconds to soften it a big.
Remove from microwave and then add in mashed bananas (or mash in the bowl). Then add in eggs, sour cream and vanilla extract, and stir.
Add the sugar to the bowl and stir, then add in flour, baking powder and baking soda and salt and stir to Incorporate. You don't want to over stir the batter, so just stir until everything is combined.
Spoon into prepared spring form pan, and then spoon the caramel sauce around the cake batter creating a swirl. Place cake pan on top of a baking sheet.
Bake for 40-45 minutes or until a toothpick comes out clean. Let cool, then slice and enjoy!