Dissolve yeast in water and let proof for a few minutes until bubbly.
Sift flour, sugar, baking powder, baking soda and salt into a medium bowl.
Add buttermilk, yeast and melted shortening to flour mixture and stir to combine.
Roll out dough about ¾" thick on a floured board. Cut with biscuit cutters and place in a cast iron skillet. Place near oven while preheating to rest and rise a bit.
Preheat oven to 425 degrees F. Bake for 10 minutes until biscuits look like they are barely baked on top. Top biscuits with bacon grease and bake for 5-10 minutes until as brown as you desire.
Notes
This makes enough for one pan of biscuits. You can double the recipe to use the full pack of yeast then shape and freeze half of the biscuits for another time. Just defrost them completely before baking for full rise in the oven (at least 30 minutes before preheating the oven).