Combine the baking soda with flour in a bowl and then you have to pulse the shortening with the sugar to turn it into a creamed mixture. This creamed mixture should be fluffy, lightweight, and soft.

Break eggs in this fluffy mixture, add the mashed bananas, and pour the buttermilk into it. Also, add the vanilla essence and the combined flour mixture to it.

Blend well and add black walnuts.

Use a cooking spray on cooking pans and transfer the mixture to these pans. Bake for more than half an hour and use cooling racks to cool it down.

Then you have to prepare the frosting for your cake. Take butter and melt the sugar in the butter in this pan. Once the sugar is melted, turn off the heat and let cool. Then add vanilla essence to it.

In this cooked sauce, blend the confectioner's sugar and add a tablespoon of oil to it.

Add a little cream and then spread the frosting over the cake in two layers like a sandwich. Put the chopped walnuts on the sides and on top of the cake.