Mix the dry ingredients (in the above order) in a bowl, and then cut in the shortening as you would for a pie crust. When it looks grainy or like little beads, it's time to stir in the buttermilk and the yeast mixture. Mix thoroughly but don't overmix.
The dough is ready to use, or it can be refrigerated in a covered bowl for later.
When ready to make biscuits, place dough on a well-floured counter or board and knead lightly.
Roll out (don't overroll or work the dough) and cut with a biscuit cutter.
Place the biscuits on a greased pan and let rise slightly--this is an important step, especially if you have refrigerated dough.