How to Make It
Combine shrimp, butter, eggs, scallions, lemon zest, 3⁄4 cup of the panko, 1 tablespoon of the lemon juice, 1 1⁄2 teaspoons of the salt, and 1⁄2 teaspoon of the paprika in a bowl. Shape into 8 (3-inch) cakes. Sprinkle remaining 3⁄4 cup panko on a large plate; gently transfer cakes to plate, pressing both sides in panko. Place cakes on a parchment paper-lined baking sheet. Cover; chill 15 minutes.
Combine mayonnaise, horseradish, 1⁄2 teaspoon of the salt, and remaining 1⁄2 tablespoon lemon juice and 1⁄4 teaspoon paprika. Set aside.
Heat 2 tablespoons of the oil in a large nonstick skillet over medium. Cook 4 cakes 4 to 5 minutes per side. Transfer to a plate lined with paper towels; sprinkle with 1⁄8 teaspoon of the salt. Wipe skillet; repeat with remaining 2 tablespoons oil, 4 cakes, and 1⁄8 teaspoon salt. Top with sliced scallions and sauce. Serve with lemon wedges.