Cream the shortening with sugar and vanilla in a bowl.
Add the eggs, one at a time, beating well after each addition.
Sift the flour, baking powder and soda together and add to creamed mixture alternately with sour cream.
Blend the butter, brown sugar, cinnamon and walnuts in a bowl.
Pour half the batter into a greased tube pan and add half the brown sugar mixture.
Bake at 350 degrees for 50 minutes, then cool.
Drizzle with confectioners' sugar icing, if desired.