1. Preheat oven to 400 degrees F. Line a cookie sheet with parchment paper. Combine flour, baking powder, sugar and salt in bowl. Cut in shortening.
2. Add mashed sweet potatoes. (I usually use sweet potatoes that I have baked or microwaved in their skin and then cooled and mashed)
3. Mix the dough together. It is unlikely that the dough will be dry; for me it is usually a little too sticky, so be sure to add some flour if that is the case. The biscuits will rise better if the dough is not very wet and sticky. You can add a little flour and/or milk to get it the right consistency. The dough will be very soft, but you do not want it to be wet and sticky.
4. Roll out on a floured board to between 3/4"-1"thickness. Cut with biscuit cutters. I use 2"-2 1/2" cutters. Place on parchment paper, and bake about 15 minutes.
I usually make these when I am serving soup or stew for dinner. My kids love them, and they don't get to eat them until after they've eaten most of the rest of their dinner.