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 tray. Freeze for 20 minutes until firm enough to handle during breading.
03 - Prepare three shallow bowls: place flour in the first, beat eggs in the second, and pour panko breadcrumbs into the third for the dredging process.
04 - Coat each chilled ball in flour, shaking off excess. Dip into beaten egg, then press firmly into panko breadcrumbs to coat completely and evenly.
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, turning occasionally, until golden brown and crispy, approximately 2–3 minutes per batch. Transfer to paper towels to drain excess oil.
07 - Whisk mayonnaise, ketchup, pickle relish, horseradish, hot sauce, smoked paprika, garlic powder, salt, and pepper until smooth and fully incorporated.
08 - Arrange warm Reuben balls on a serving platter alongside spicy Thousand Island sauce for dipping.