1Mix butter, shortening, egg yolks and vanilla. Thoroughly blend in cake mix 1/3 at a time.
2If dough is dry add 1 to 1/2 teaspoons water. Half cup chopped nuts, chocolate morsels, coconut, or raisins can be added to dough.
3Roll dough into long smooth roll and chill until firm.
4Preheat oven to 375 degrees F (190 degrees C).
5Slice cookies about 1/4 inch thick and bake on ungreased cookie sheet about 8 minutes or until cookie is light brown around edges. Cool cookie on sheet about 1 minute before removing to rack.