Preheat oven to 425°. Line a baking sheet with parchment paper or a non-stick liner.
Pierce each sweet potato with sharp knife once. Place potatoes on baking tray and roast for 30-40 minutes, until a sharp knife pierces through potatoes easily. When in doubt, bake for 5-10 minutes more. They should be as easy to cut through as butter.
Remove potatoes from oven and reduce oven temperature to 375°. Let potatoes sit until just cool enough to handle, but still hot. Scoop flesh from slightly cooled potatoes into food processor or mixer bowl. Mix on medium until pureed.
Meanwhile, measure flour, sugar, salt and baking powder into separate bowl. Stir with a fork to combine.
Once potatoes are pureed, measure 1 3/4 cups of puree. (Set aside any remaining puree to add to pancakes, muffins, or cookies.) Place the 1 3/4 cups of puree back in mixing bowl with butter pieces, and mix on medium until the butter is melted and incorporated.
Add the dry ingredients slowly to the sweet potato mixture, until fully incorporated. Slowly sprinkle in flour until the dough is just dry enough that it doesn’t stick to everything it touches.
Shape into biscuits and bake at 375° for 17-20 minutes or until bottoms and edges begin to turn golden brown. Remove from oven and serve warm with butter.