Preheat oven to 350 °F. Grease and flour two 9-inch cake pans.
For the cake: In a medium bowl, whisk together flour and baking soda; set aside.
Using an electric mixer, cream together shortening and granulated sugar in a bowl until light and fluffy, about 2 to 3 minutes.
Add eggs 1 at a time, mixing well after each addition.
Mix in mashed bananas, buttermilk and 1 teaspoon vanilla.
Add flour mixture, and mix until just combined.
Stir in 1 cup black walnuts.
Pour into prepared pans. Bake for 35 minutes. Cool in pans on a cooling rack for 10 minutes. Remove from pans and cool completely.
<br>Cream Cheese Frosting:</br>
Combine butter and cream cheese in the bowl of a stand mixer (or you may use an electric mixer) and beat until creamy, well-combined, and lump-free.
Add vanilla extract and salt and stir well to combine.
With the mixer on low, gradually add powdered sugar until completely combined.
Use to frost completely cooled cake or cupcakes.
Place one cake layer onto a serving plate and spread a thick layer of frosting evenly to the edges of the cake layer.
Place the second layer on top of the other iced layer and press gently.
Ice the top and sides of the cake until completely covered and smooth as desired.
Surround sides and sprinkle the top of the cake with 2 cups crushed black walnuts.