Preheat the oven to 375F degrees. Spray 9x13-inch baking dish with nonstick cooking spray.
In a medium bowl, cream together sugar, sour cream, egg, and melted butter.
Add mashed bananas and vanilla extract and continue to mix.
Add flour and baking soda; mix well.
Pour batter into baking dish.
Bake for 25-35 minutes until a toothpick inserted in the center comes out clean. Cool completely before frosting.
For the frosting:
Cream butter and confectioner's sugar together until smooth using an electric hand mixer or stand mixer.
Slowly add the heavy cream; stir until smooth. Stir in vanilla extract.
Spread on cooled cake. Slice then serve!
Video
Notes
The frosting really is optional in this. This cake is so moist and is plenty sweet all by itself. It will be more like a snack cake without the frosting.