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 the mixture into 1-inch balls and arrange on a parchment-lined baking sheet. Freeze for 20 minutes until firm enough to handle without falling apart.
03 - Arrange three shallow bowls: place flour in the first, beaten eggs in the second, and panko breadcrumbs in the third. Line them up in assembly order for efficient coating.
04 - Dredge each chilled ball in flour, shaking off excess. Dip into egg mixture, allowing excess to drip off, then press firmly into panko breadcrumbs to coat completely. Return to the lined tray.
05 - Pour vegetable oil to a depth of 2 inches in a deep skillet or saucepan. Heat to 350°F, maintaining temperature throughout frying.
06 - Fry balls in batches of 6-8, turning occasionally with a slotted spoon, until golden brown and crispy, approximately 2-3 minutes per batch. Transfer to paper towels to drain excess oil.
07 - Whisk together mayonnaise, ketchup, pickle relish, horseradish, hot sauce, smoked paprika, garlic powder, salt, and pepper until completely smooth and well combined.
08 - Arrange Reuben balls on a serving platter and serve immediately while warm, accompanied by spicy Thousand Island sauce for dipping.