Heat a large skillet over medium heat. Add the chopped corned beef and cook for 4–5 minutes, stirring occasionally, until warmed through and lightly crispy around the edges. Remove from heat and let cool slightly.
¾ lb. corned beef
In a large bowl, combine the crispy corned beef, chopped Swiss cheese, and well-drained sauerkraut. Mix until evenly combined.
6 slices swiss cheese, ½ cup sauerkraut
Lay an egg roll wrapper on a clean surface with one corner pointing toward you. Spoon about 2–3 tablespoons of filling into the center.
2 egg roll wrappers
Fold the bottom corner over the filling, then fold in the two side corners. Roll tightly toward the top corner. Brush the top corner with beaten egg and press to seal. Repeat with the remaining wrappers and filling.
1 egg
Heat 2–3 inches of oil in a heavy-bottomed pot or deep skillet to 350°F.
oil for frying
Fry the egg rolls in batches for 3–4 minutes, turning occasionally, until golden brown and crispy on all sides. Do not overcrowd the pan.
Transfer to a paper towel-lined plate or wire rack to drain.
To make the Reuben sauce, whisk together the mayonnaise, ketchup, relish, Dijon mustard, paprika, and black pepper in a small bowl until smooth.
½ cup mayo, 2 tbsp ketchup, 1 tbsp relish, 1 tsp dijon mustard, pinch of paprika, black pepper
Serve the hot egg rolls with the creamy Reuben sauce for dipping.