1. Preheat your oven to 350°F and grease a 9×13 inch baking pan.
2. In a mixing bowl, beat butter and sugar until light and fluffy.
3. Add eggs, sour cream, and vanilla extract, mixing until well combined.
4. In a separate bowl, whisk together flour, baking soda, and salt.
5. Gradually add the dry ingredients to the wet ingredients, mixing gently.
6. Fold in the mashed bananas until evenly incorporated.
7. If using, fold in chopped walnuts or chocolate chips.
8. Pour the batter into the prepared pan and spread evenly.
9. Bake for 25-35 minutes or until a toothpick inserted in the center comes out clean.
10. Let the cake cool completely in the pan before adding frosting.
11. For the frosting, beat softened cream cheese and butter until smooth.
12. Add powdered sugar and vanilla extract, then mix until combined.
13. Gradually add heavy cream and continue beating until fluffy.
14. Spread frosting evenly over the cooled cake.
15. If desired, garnish with banana slices and chopped walnuts.
16. Store covered in the refrigerator until ready to serve.
17. Slice and enjoy your banana bread cake with cream cheese frosting.