Crispy fried egg roll wrappers stuffed with tender corned beef, cabbage, Swiss cheese, and a smear of whole grain mustard - these are the St. Patrick's Day appetizer that'll disappear before the main course hits the table. Crunchy outside, savory and melty inside. Dip them in Russian dressing and it's basically a Reuben you eat with your hands.
In a medium skillet over medium heat, add 1 tsp oil and sauté the diced onion, cabbage, and carrot with 1/2 tsp salt and 1/4 tsp black pepper for 3–5 minutes, just until cabbage softens and moisture evaporates. This pre-cooking prevents soggy egg rolls later.
Transfer the vegetable mixture to a bowl. Stir in the chopped corned beef and shredded Swiss cheese until evenly distributed. The cheese acts as a binder and flavor booster.
Lay one egg roll wrapper on a clean dry surface. Spread a scant 1/2 tsp whole grain mustard in the center. Top with 2–3 generous tbsp of filling. Fold bottom up over filling, tuck sides, and roll tightly, sealing the edge with a dab of water. Repeat with remaining wrappers and filling.
Pour vegetable oil into a large, deep pan to 1.5 inches depth. Heat to 350°F — hot oil ensures a crisp shell, not a greasy one (test: a small scrap should bubble vigorously).
Fry egg rolls in batches, turning occasionally, until golden-brown on all sides, about 2–3 minutes per batch. Drain on a paper towel–lined rack. Let cool 2 minutes before serving, so the cheese can set slightly and filling is not molten.