01 - Grate the starchy potatoes using the large holes of a box grater. Place in a clean tea towel and squeeze out as much liquid as possible; discard liquid.
02 - Boil the waxy potatoes in salted water until just tender, about 10–12 minutes. Drain thoroughly and mash until smooth.
03 - In a large bowl, combine grated raw potato, mashed potato, flour, baking powder, salt, and pepper. Mix until evenly incorporated.
04 - Stir in melted butter and milk until a thick, spreadable batter forms.
05 - Heat a large non-stick skillet or griddle over medium heat and add a knob of butter.
06 - Drop large spoonfuls (about 1/4 cup each) of batter onto the skillet, flattening each slightly with the back of the spoon.
07 - Cook 3–4 minutes per side, until golden brown and crisp. Fry in batches as needed, adding more butter if necessary.
08 - Serve hot, topped with sour cream and a sprinkle of chives or scallions if desired.