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 inch fluted tube pan. Bake at 350 degrees for 50 minutes or until a toothpick comes out clean. Cool 10 minutes in pan before removing to a wire rack to cool completely. Dust with confectioners sugar.