With electric mixer at high speed, cream butter, shortening til soft. Add sugar gradually, continuing to cream about 5 minutes til light and fluffy. Add egg, vanilla; beat well. Sift flour, baking powder, salt together; add in 3 additions by hand or with electric mixer, mix well after each addition, dough will be stiff. Shape dough into 2 rolls, wrap in plastic film, foil or waxed paper, refrigerate at least 1 hr. Then dough is ready to put into cookie gun. Bake 7-8 minutes at 375 degrees or til just starting to turn light golden around edges, don't overbake!