1. Preheat oven to 450 degrees Fahrenheit. Place 12 inch skillet in the oven to preheat.
2. Add flour to a large mixing bowl. Grate chilled butter into the flour. Whisk together buttermilk and sweet potato and add to the flour mixture. Turn out onto a lightly floured surface and quickly pat to a rectangle about ½-¾-inch thick.
3. Lightly dust the surface of the dough with flour from your fingertips and fold the sheet of dough into thirds, similar to folding a business letter. Repeat patting, dusting, and folding seven times—or fewer if you feel the dough begin to tighten.* The final time, pat the dough to a rectangle slightly larger than the size of your skillet. Using a round biscuit cutter or a drinking glass, cut into about 13 round biscuits.
4. Remove preheated skillet from the oven. Drop shortening onto the skillet and return to the oven for 2 minutes. Remove skillet again and place each biscuit into the skillet, and immediately turn them over to coat with shortening.
5. Top with sage ribbons. Return to oven and reduce temperature to 425 degrees Fahrenheit. Bake until golden brown, 12–18 minutes.
6. Brush with melted butter before serving.

Pro Tip: Careful not to overwork the dough; overworked dough makes for a tough biscuit.