How to Make It
Place hash browns, onion, flour, eggs, 2 teaspoons of the salt, and 1 teaspoon of the pepper in a large bowl and toss to combine.
Heat 2 tablespoons oil in a large cast-iron skillet over medium-high. Working in batches, drop spoonfuls of hash brown mixture (about 2 tablespoons per latke) into skillet, flattening with a spatula. Cook, turning once, until browned on both sides, about 5 minutes per side. Transfer to paper towels to drain. Repeat with remaining oil and hash brown mixture (you should have about 32 latkes).
Stir together mayonnaise, chives, horseradish, remaining ½ teaspoon pepper, and ¼ teaspoon salt until combined. Build sliders with latkes, brisket, and horseradish sauce.