Using the large holes of a box grater/shredder, shred the potatoes into a mixing bowl. Grate in the onion.
With your hands, squeeze out as much liquid as possible from the mixture, picking it up a handful at a time, squeezing over the sink, and then transferring the squeezed handful to another bowl. Add the egg, flour, baking powder, salt and pepper. Stir with a fork until well blended.
In a large, heavy skillet, heat about 1 inch of cooking oil over high heat to 350 F on a deep-frying thermometer. With a metal tablespoon, carefully place a spoonful of the mixture into the hot oil, pressing it down slightly with the back of the spoon to form an evenly thick pancake about 3 inches in diameter. Add more spoonfuls, taking care not to overcrowd the skillet. Cook the pancakes until golden brown, 2 to 3 minutes per side, turning them over carefully with a slotted metal spatula. Transfer to a tray or platter lined with paper towels to drain. Continue with the remaining mixture.
Meanwhile, in a small bowl, stir together the crémé fraiché or sour cream and dill. Season to taste with lemon juice, salt and pepper.
To serve, put the potato pancakes on a platter. Spoon a small dollop of the crémé fraiché mixture onto each pancake and top with flakes of whitefish. Serve immediately. - Tribune Media Services.