Preheat oven to 450°.
Sift together flour, sugar, baking powder and salt.
In a large mixing bowl, mash sweet potatoes with a potato masher.
And softened butter and mash until butter dissolves into the sweet potatoes.
Add flour mixture to the potato mixture and stir to make until a soft dough forms.
Add milk, a tablespoon at a time.
Use only as much as necessary to get the ingredients to adhere.
Turn dough out onto a floured board and knead lightly until dough looks smooth—1-2 minutes.
Roll dough out to 1-inch thickness.
Cut dough with a biscuit cutter or glass.
Spray cookie sheets or glass baking dish with cooking spray.
Place biscuits on prepared baking sheets.
Brush melted butter on tops and sides of biscuits.
Bake about 15-20 minutes or until done.
(Because I made my biscuits a lot thicker than the original recipe called for, they took 22 minutes to bake.)
Brush biscuits with melted butter again after removing from oven.