How to Make It
Whisk the eggs, flour, salt, pepper, horseradish, and capers in a bowl until combined.
Shred the onion using the large holes of a box grater or the grating attachment of a food processor.
Shred the potatoes using the large holes of a box grater or the grating attachment of a food processor.
Working in batches, place the potatoes and onions in a dish towel, and squeeze out as much excess liquid as possible. Add the potatoes and onions to the egg mixture, and toss with your hands to combine.
Heat oil in a skillet over medium heat. Once oil is hot, drop the potato batter into the pan by the heaping spoonful, keeping the pancakes about two inches apart.
Flatten each latke with the back of a spoon and cook until golden brown, two to three minutes per side. Transfer to a paper towel-lined tray to drain.
Serve warm with smoked salmon and sour cream.