Sift together dry ingredients. Cut in shortening. Blend in sweet potatoes. Add enough milk to make a soft dough (this will depend on moisture in potatoes).
Knead lightly. Roll ½″ thick on lightly floured board. Cut with floured 2″ biscuit cutter.
Place on ungreased baking sheet and bake in hot oven (400°) 20 minutes, or until brown.