Mix all dry ingredients. Cut in Shortning. Add Buttermilk and Yeast mixture. Let rise in a warm place if you want to bake them sooner. If not they will keep in the refrigerator as long as you want. Take risen dough and pat out to 1 inch thick on a floured board. Cut with a floured biscuit cutter. Bake 12 to 15 minutes on a greased cookie sheet or pan in a 400 degree oven.