In a small bowl, mix the mashed banana with the lemon juice and zest. Set aside.
In a medium bowl, mix flour, baking soda and salt, set aside.
In the bowl of an electric stand mixer, cream ¾ cup butter and 2 1/8 cups of sugar until light and fluffy.
Beat in eggs, one at a time, then mix in 2 tsp vanilla.
Beat in the flour mixture alternately with the buttermilk.
Stir in banana mixture. Pour batter into the prepared pan and bake in preheated oven for one hour or until a toothpick inserted in the center comes out clean.
Remove from oven and place directly into the freezer for 45 minutes.
Frosting
Cream the butter and cream cheese together until smooth. Beat in 1 teaspoon of vanilla. Add powdered sugar and beat on low speed until combined, then on high speed until the frosting is smooth. Spread on cooled cake.
Sprinkle chopped walnuts over top of the frosting, if desired.
This recipe was calculated using the exact brands and measurements I used to make this recipe. If you are following a strict diet please note changing anything will cause the nutritional info to change. My calculations are intended as a guide only.