Preheat your oven to 350 degrees F. Grease and flour a 9x13 pan.
In a separate bowl, mix the mashed bananas with a tablespoon of lemon juice and set aside.
In a large mixing bowl, stir together vegetable oil and granulated and brown sugar. Add the eggs one at a time, stirring well after each addition. Add a teaspoon of vanilla and mix well.
Add salt, baking soda and 1 cup of the flour to the large mixing bowl and stir to combine. Add buttermilk and remaining flour and gently stir to combine.
Fold in the bananas, and pour into the prepared 9x13 pan.
Bake at 350 degrees for 40 minutes or until a toothpick inserted into the center comes out clean or with just a few moist crumbs.
Let the cake cool completely, then frost with the Cream Cheese Frosting (below).
Cream Cheese Frosting
Cream together the 8 ounces of cream cheese and 1/3 cup of butter until fluffy.
Add 3 cups of powdered sugar and mix well.
Blend in the vanilla extract and add up to an extra 1/2 cup of powdered sugar until your desired consistency is reached. Spread onto the cooled cake.
The finished and frosted cake needs to be stored in the fridge. Wrap the pan in plastic wrap and it will keep fresh for up to 3 days. Without the frosting the cake freezes very well. Wrap tightly in plastic wrap and freeze for up to 2 months. Thaw overnight in the fridge then bring to room temperature before frosting and serving.