01 - Combine chopped corned beef, sauerkraut, Swiss cheese, cream cheese, Dijon mustard, and black pepper in a large bowl. Mix until all ingredients are evenly incorporated.
02 - Shape the mixture into 1-inch balls and arrange on a parchment-lined baking tray. Freeze for 20 minutes to firm the texture for easier handling.
03 - Arrange three shallow bowls: place flour in the first, beat eggs in the second, and pour panko breadcrumbs into the third.
04 - Dredge each chilled ball in flour, then dip into beaten egg, ensuring full coverage. Finally, coat completely with panko breadcrumbs, pressing gently to adhere.
05 - Pour vegetable oil to a depth of 2 inches in a deep skillet or saucepan. Heat to 350°F, monitoring temperature with a kitchen thermometer.
06 - Fry balls in batches, turning occasionally to ensure even browning. Cook for 2–3 minutes per batch until golden brown and crispy. 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 smooth and fully combined.
08 - Arrange warm Reuben balls on a serving platter alongside spicy Thousand Island sauce. Serve immediately while crispy.