Sift flour, baking powder, granulated sugar, and salt in a large mixing bowl.
Quickly grate frozen butter into the bowl of flour. Alternatively, you quickly cut butter into flour mixture with a pastry blender until the mixture resembles coarse crumbs; this might take about 5 minutes. Your flour should be crumbly with pea-size chunks. Let the bowl rest in the fridge if there is any wait time.
Make a well in the center of the bowl, add mashed sweet potatoes, and stir until it barely comes together. DO NOT OVER-MIX because you want those flakes. Let the dough rest in the fridge for about 10 minutes while you prepare your work surface.
Sprinkle flour onto a board or clean surface. Remove the dough from the fridge and place it on the board. Knead 3-4 times - just enough for it to come together. You will still see flakes of butter in the dough. Again don't overmix.
Gently, gently pat the dough with your hands or roll it out to about ½″ thick.
Fold the dough, repeating the folding process 6-8 times. This ensures flakiness, so go easy on the rolling process. After the folding is complete, gently press the dough down to 1 inch thick, ready to be cut.
Use a 2- or 3-inch round cookie cutter or a rim of a glass to cut out the biscuits. Firmly push it straight down, then pull it up. Use your fingers to gently loosen the dough from the cutter and space them out equally across your prepared baking sheet.
Knead any leftover scraps of dough and repeat until all of the dough is used up. They might not look as pretty as the rest, but they will pass the taste test.
Lightly brush with buttermilk or cream.
Bake at 400℉/205℃ for 12-15 minutes or until lightly browned. While they are baking, melt the butter.
Remove the biscuits from the oven, immediately brush them with melted butter, and serve with honey if desired.