Preheat the oven to 425 degrees and line a baking sheet with parchment paper to prevent sticking.
Cook the sweet potatoes in the microwave. Clean the outer layer then prick with a form all over. Wrap in a paper towel and place in a bowl that is microwave-safe for about 5 minutes or so. You may need to do more time depending on the size. Once the potato has cooked and cooled, peel the skin and mash with a fork.
Pour 1/3 cup of milk with the mashed sweet potato and stir.
Put the flour, sugar, baking powder, and salt into a food processer and pulse. Add in the butter and pulse. The mixture will look very coarse. Add in the potato and milk mixture and pulse to combine. (Don't overmix, just pulse until combined)
Add the rest of the milk a tiny bit at a time until the mixture is moist and starts to stick together.
Put some flour on the counter and put the dough on top. Fold it 2-3 times and pat the dough until it's about 1/2 inch in thickness.
Use a biscuit cutter and cut the dough into 2-2 1/2 inches in size.
Put the biscuits on a baking sheet and bake in the oven for 12-14 minutes.