Step 1

Heat oven to 350°. Prepare a 9x13 baking dish and spray with cooking spray. Set aside.

Step 2

In a large bowl with a hand mixer, or use a stand mixer with a paddle attachment, cream butter and sugar together until light and fluffy. The mixture will look crumbled but beat it for a couple minuntes and it will start to look fluffy.

Step 3

Add eggs, sour cream, and vanilla. Blend together until combined and creamy.

Step 4

Add flour, baking soda, and salt. Blend on low speed just until combined.

Step 5

Add mashed banana and gently stir together. Dump batter into the baking dish and spread out evenly.

Step 6

Cook for 25-35 minutes or until toothpick inserted in middle comes out with moist crumbs or nothing at all. If a toothpick comes out with wet batter then you need to cook it slightly longer. The edges and top will be light browned.

Step 7

Let cake cool completely before frosting.Once cake is cooled you can either frost it right away and serve OR cover it tightly with tin foil and let it sit at room temperature overnight and then frost it before serving.

Step 8

In a large bowl, beat butter and cream cheese together until combined. Add in vanilla extract, powdered sugar, and heavy cream. Beat together, starting on low speed and increase as needed, until frosting forms. Add more powdered sugar and/or milk until desired frosting consistencey is reached. I never have to add more milk or powdered sugar than what's called for. You want the frosting really thick so it will cut nice. * NOTE: If you use anything other than heavy whipping cream start with 1 tablespoon and work from there. Heavy cream is so thick that you need more of it, lower fat milks you will need less of.

Step 9

Cut into squares and garnish each piece with banana slices and chopped walnuts.