Preheat oven to 350 degrees. Lightly spray a 9x13" pan with non-stick baking spray. Set aside.

In a large mixing bowl, mash the ripe bananas using a fork or potato masher. Add the sugar, vegetable oil, sour cream, eggs and vanilla. Mix well using a whisk or hand mixer.

To a second bowl, mix together the dry ingredients; flour, baking powder, baking soda and salt. Use a fork or whisk to mix together, helping to break up any lumps.

Gradually add the dry ingredients to the wet ingredients. Use a whisk or hand mixer to mix the batter. If adding nuts, fold them into the batter using a rubber scraper.

Pour the batter into the prepared pan. Bake the cake at 350 degrees for 32-35 minutes to golden brown. Test for doneness by inserting a toothpick into the center of the cake. If it comes out clean and crumb free it is done. Let cake cool completely to room temperature before frosting.

For the cream cheese frosting: place the room temperature cream cheese and butter into mixing bowl. Cream together with a hand or stand mixer. Add in the vanilla. With mixer on low speed, gradually add the powdered sugar one cup at a time, stopping to scrape down the sides of the bowl. Frosting will be thick, but not overly firm. Spread evenly onto the cooled cake. Top with additional chopped nuts and/or banana slices, if desired.