01 -
Heat oven to 350°. Prepare a 9x13 baking dish and spray with cooking spray. Set aside.
02 -
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 minutes and it will start to look fluffy.
03 -
Add eggs, sour cream, and vanilla. Blend together until combined and creamy.
04 -
Add flour, baking soda, and salt. Blend on low speed just until combined. Add mashed banana and gently stir together.
05 -
Dump batter into the baking dish and spread out evenly. Cook for 25-35 minutes or until toothpick inserted in middle comes out with moist crumbs or nothing at all.
06 -
In a large bowl, beat butter and cream cheese together until combined. Add vanilla extract, powdered sugar, and heavy cream. Beat together, starting on low speed and increase as needed, until frosting forms.
07 -
Once cake is completely cooled, frost it. Cut into squares and garnish each piece with banana slices and chopped walnuts if desired.