How to Make It
In a small bowl, combine the sour cream with 2 tablespoons of the grated red onion, 1 tablespoon of the dill and the capers; cover and refrigerate.
In a colander set in the sink, combine the remaining 1/2 cup of grated red onion with the parsnips and potato. Let stand for 15 minutes, then squeeze to remove any excess liquid. Transfer the vegetables to a medium bowl and add the egg, flour, baking powder, salt and pepper. Mix thoroughly.
Preheat the oven to 300°. Heat 1/8 inch of vegetable oil in a large cast-iron skillet. Drop rounded tablespoons of the pancake batter into the skillet, spacing them evenly and pressing lightly to flatten. Cook the pancakes over moderate heat until browned and crisp, about 4 minutes per side. Drain the pancakes on a paper towel-lined platter, then transfer them to a baking sheet and keep warm in the oven.
Arrange 4 pancakes on each plate. Place 1 1/2 to 2 ounces of the smoked fish and a dollop of caper sour cream alongside. Garnish with the remaining dill and minced red onion and serve.