Preheat oven to 350°F.
Line a 9x13" pan with parchment paper and spray with nonstick cooking spray. Set aside.
In a large bowl, combine cake mix, pudding pack, sugar, water, eggs, and sour cream. Mix until well combined.
Mash bananas very well, until pureed. (Big banana chunks keep the cake from being as light.)
Add mashed bananas and fold in with a large spoon, until well incorporated.
Pour cake batter into prepared pan. Bake for 45-50 minutes until cake springs back to the touch in the center. Bananas are heavy in a cake so if you're unsure to whether it's done, bake it for 5 extra minutes. Hard to overbake this with all the banana and eggs.
Remove from oven and let cool for 15-20 minutes before cutting.
Cut into squares. Serve and enjoy!