Preheat the oven to 400 degrees. In a medium bowl, stir the flour, baking powder, sugar and salt. Work in the shortening until pieces of shortening are tiny crumbs. Mix in the white sweet potatoes, and enough of the milk to make a soft dough.
On a floured surface, roll or pat the dough to 1/2 inch thickness. Cut into circles using a biscuit cutter or the greased edge of a drinking glass. Place biscuits 1 inch apart onto a greased baking sheet.
Bake for 12 to 15 minutes or until golden brown.