Preheat oven to 350°F. Grease a 9x13-inch baking pan and set aside.
Add the sugar and oil to a large bowl, and mix well until combined.
1½ cups granulated sugar, ¾ cup vegetable oil
Add in the eggs, mashed bananas, buttermilk, and vanilla. Whisk until combined.
3 large eggs, 1½ cups mashed bananas, ½ cup buttermilk, 2 teaspoons pure vanilla extract
In a separate bowl, combine the the flour, baking soda, baking powder, cinnamon, and salt.
3 cups all-purpose flour, 1 teaspoon baking soda, 1 teaspoon baking powder, ½ teaspoon ground cinnamon, ½ teaspoon kosher salt
Add the flour mixture to the wet ingredients, gently folding it in until just combined.
Transfer the batter to the prepared baking pan.
Bake for 30-35 minutes, or until a toothpick inserted comes out clean.
Let the cake cool completely before frosting.
To make the frosting, using a hand mixer, beat the cream cheese, butter, vanilla, and salt together.
8 ounces cream cheese, ¼ cup unsalted butter, 1 teaspoon pure vanilla extract, ⅛ teaspoon kosher salt
Beat in the powdered sugar, little by little, until incorporated.
2½ cups powdered sugar
Spread the frosting over the cake.
Top with chopped walnuts and banana slices if desired.
Chopped walnuts, Banana slices