01 - Place peeled potatoes in a large pot and cover with cold, salted water. Bring to a boil and simmer for 12-15 minutes until fork-tender. Drain thoroughly.
02 - Mash the potatoes until completely smooth. Stir in the butter and milk while the potatoes are still hot. Let cool for 5 minutes.
03 - Add the sliced scallions, flour, salt, and pepper to the cooled mash. Mix until a soft, slightly sticky dough forms, being careful not to overmix.
04 - Lightly flour your work surface. Turn out the dough and gently knead until just combined. Roll or pat out to 1/2 inch thickness.
05 - Cut into rounds using a 3-inch cutter or shape into rough rounds by hand.
06 - Heat a large non-stick skillet over medium heat and melt a knob of butter. Cook potato cakes in batches for 3-4 minutes per side until golden and crisp. Add more butter as needed between batches.
07 - Serve hot, garnished with extra scallions or a dollop of sour cream if desired.