01 - Combine chopped corned beef, sauerkraut, Swiss cheese, cream cheese, Dijon mustard, and black pepper in a large bowl. Mix thoroughly until all ingredients are evenly distributed.
02 - Shape the mixture into 1-inch balls and arrange on a parchment-lined baking tray. Freeze for 20 minutes to firm up for easier handling during breading.
03 - Arrange three shallow bowls: place flour in the first, beat eggs in the second, and pour panko breadcrumbs into the third.
04 - Coat each chilled ball first in flour, shaking off excess. Dip into beaten egg, then press firmly into panko breadcrumbs to ensure complete coverage.
05 - Pour 2 inches of vegetable oil into a deep skillet or saucepan. Heat to 350°F over medium-high heat.
06 - Fry balls in batches, turning occasionally, until golden brown and crispy, about 2–3 minutes per batch. Remove with a slotted spoon and drain on paper towels.
07 - Whisk together mayonnaise, ketchup, pickle relish, horseradish, hot sauce, smoked paprika, garlic powder, salt, and pepper until completely smooth and well combined.
08 - Serve the fried Reuben balls warm while crispy, accompanied by the spicy Thousand Island sauce for dipping.