01 - Combine chopped corned beef, sauerkraut, Swiss cheese, cream cheese, Dijon mustard, and black pepper in a large bowl. Mix until evenly blended and cohesive.
02 - Roll mixture into 1-inch balls and place on parchment-lined tray. Freeze for 20 minutes until firm enough to handle without breaking apart.
03 - Arrange three shallow bowls: place flour in first, beat eggs in second, and pour panko breadcrumbs into third. Keep bowls close to cooking area for efficient assembly.
04 - Coat each chilled ball thoroughly in flour, shaking off excess. Dip in beaten egg, allowing excess to drip off, then press into panko crumbs to coat completely.
05 - Pour 2 inches vegetable oil into deep skillet or saucepan. Heat to 350°F, maintaining temperature throughout cooking process for even browning.
06 - Fry balls in batches of 5-6, turning occasionally, until deep golden brown and crispy, about 2-3 minutes per batch. Transfer to paper towel-lined plate to drain excess oil.
07 - Whisk together mayonnaise, ketchup, pickle relish, horseradish, hot sauce, smoked paprika, garlic powder, salt, and pepper until smooth and fully incorporated.
08 - Arrange warm balls on serving platter alongside spicy Thousand Island sauce. Serve while hot and crispy for optimal texture.