Preheat the oven to 400 degrees F (200 degrees C).
In a medium bowl, stir together the flour, baking powder, sugar and salt. Cut in the shortening until pieces of shortening are pea-sized or smaller. Mix in the sweet potatoes, and enough of the milk to make a soft dough.
Turn dough out onto a floured surface, and roll or pat out to 1/2 inch thickness. Cut into circles using a biscuit cutter or a drinking glass. Place biscuits 1 inch apart onto a greased baking sheet.
Bake for 12 to 15 minutes in the preheated oven, or until golden brown.