Cream together butter, eggs, and sugar. Add vanilla and buttermilk.
Mix dry ingredients together and add to the creamed mixture.
Add bananas and ½ cup chopped walnuts. Mix well.
Pour into 2 (or 3 small) well-greased cake pans.
Bake at 350 for 35-40 minutes.
Cool for 15 minutes and remove from pans. Frost the cake and serve!
FROSTING:
With hand mixer, combine cream cheese and butter until smooth. Add vanilla and lemon zest, continuing to mix. Add in powdered sugar ½ cup at a time. Mix until smooth.
Divide frosting into thirds in between each cake layer making sure to push frosting in large globs (not smooth) to the edges of the cake. Once frosting is done, sprinkle walnuts on top and place cake in refrigerator for at least an hour, allowing frosting to harden slightly (this makes cutting the cake much easier).