In a mixing bowl, cream the shortening and sugar. Add the eggs, one at a time, beating well after each addition. Blend in vanilla. Add bananas and mix well. Combine flour, baking powder, baking soda and salt; add to the creamed mixture alternately with sour cream, stirring just until combined. Stir in walnuts. Pour into a greased and floured 10-in. fluted tube pan. Bake at 350 degrees F for 50 minutes or until cake tests done. Cool 10 minutes in pan before removing to a wire rack to cool completely. Dust with confectioners' sugar before serving.