Classic Polish diamond-shaped potato dumplings ('little hooves') made with cooked riced potatoes and flour, boiled tender and tossed in foaming butter or pan-fried until golden and crispy.
Place the cooled riced potatoes on a clean board. Add the plain flour, potato starch, egg, and salt. Quickly knead the ingredients together into a cohesive, smooth dough without overworking, which can make the dumplings heavy.
Dust the board lightly with flour. Divide dough into 4 pieces. Roll each piece into a rope approximately 2cm thick. Flatten slightly with your palm, then cut diagonally at a 45-degree angle into 3cm diamond lozenges ('little hooves').
Drop the dumplings in batches into a wide pot of boiling salted water. Stir gently with a wooden spoon so they do not stick to the bottom. Cook for 2 minutes after they float to the top, then lift out with a slotted spoon.
Toss the freshly poached kopytka directly in melted butter, or optionally pan-fry them in a skillet until crisp and golden brown on both sides. Serve topped with caramelised onions or savoury roast gravy.