• Preheat the oven to 350 degrees F. Grease a sheet pan (18" x 13" x 1"). Set aside.
• In a large bowl, cream together butter and sugar until light and fluffy, about 5 minutes. Beat in eggs, bananas, and vanilla. Switch to low speed and add buttermilk then blend until combined. Add flour, baking soda, and salt. Mix until just combined.
• Pour batter into greased pan. Bake 16-25 minutes, until a toothpick inserted into the center, comes out clean. Cool completely.

Toast the Walnuts (optional)

• Preheat the oven to 350 degrees F. Arrange walnuts in a single layer on a parchment-lined baking sheet. Bake uncovered for 8-10 minutes, watching carefully.
• Cool completely before finely chopping nuts.

Make the Cream Cheese Frosting

• In a medium bowl, cream together butter and cream cheese using an electric mixer. Add vanilla then slowly add in powdered sugar, beating until light and fluffy.
• Spread frosting all over the cooled cake. Top with chopped nuts.