Preheat oven to 350 degrees F. Grease a 13"x18" sheet pan with non-stick spray and set aside.
Mash the bananas in a bowl with a fork until smooth, then set aside.
In a separate bowl whisk together the flour, baking powder, baking soda, cinnamon and salt. Set aside.
To the bowl of a stand mixer, beat the butter with a paddle attachment for about 1 minute, until it's nice and creamy. Add in the sugar and brown sugar and beat an additional 2 minutes until creamy. Add in the eggs one at a time, while still beating on low speed. Blend in the vanilla extract. Scrape down the sides of the bowl as needed.
Add the mashed bananas to the wet ingredients and mix well. Finally, alternate adding in ⅓ of the flour mixture, then ⅓ of the buttermilk to the wet ingredients, beating well in between. Mixture will be slightly lumpy and that's ok.
Spread the batter evenly into the prepared pan and bake for 30 to 35 minutes, or until a toothpick inserted in the center comes out clean. Remove from oven and set on a wire rack to cool completely.
For The Frosting:
Beat together the cream cheese and butter until light and creamy. Add in the vanilla extract, cinnamon and salt and mix.
Add the powdered sugar to the bowl and mix slowly until it's incorporated, then increase speed and beat for an additional 2 minutes until it's light and fluffy.
Spread frosting evenly over the cooled cake. Cover and store cake in the fridge until ready to serve. Enjoy!
Notes
Since the frosting contains cream cheese, this cake should be stored in the refrigerator for optimal freshness.