Pre-heat the oven to 275 degrees. Grease 2, 8” round baking pans.
In a small bowl mix mashed bananas and lemon juice. Set aside. In a medium bowl mix flour, baking soda, and salt. Set aside. In a large bowl cream ¾ cups butter and 2 1/8 cups sugar until light and fluffy.
Beat in eggs one at a time. Stir in vanilla extract. Beat in the flour mixture alternately with the buttermilk. Stir in banana mixture.
Evenly pour batter into 2, 8” round baking pans. Bake for 1 hour to 1 hour and 30 minutes or until a toothpick comes out clean. Between those times keep checking on the cake with a toothpick to see if it’s done. When the cake is done take the baking pans and place them directly into the freezer for 45 minutes to cool.
While the cake is cooling, to make the frosting- In a bowl cream the butter and cream cheese until smooth. Beat in vanilla extract. Add the icing sugar a little at a time and beat on low until combined. Then beat on high until smooth.
Remove the cake from the pans and lay out the bottom half on a plate. Spread it fully with frosting. Add the top half and cover the entire cake with frosting. Add chopped walnuts on top.