Cream butter, add sugar, then eggs. Dissolve soda in boiling water. Add this to mashed bananas. Sift flour, salt and baking powder together. Add flour alternately with bananas. Then add chopped walnuts. Bake in 2 layers in moderate oven 375 degree F. or in 9×13″ cake pan at 350 degrees. Bake 25 minutes for layer cake and 35 to 40 minutes for 9×13″ cake. Put cream filling between layers and a layer of sliced bananas. Ice all over with white icing and decorate with sliced bananas.