In a large pot, bring water to a rolling boil. Submerge the cabbage, carrots, and celery in the boiling water, allowing them to blanch for approximately two minutes. Promptly transfer the vegetables into an ice bath to halt the cooking process. Drain thoroughly and use a clean kitchen towel to extract any excess moisture. Ensuring the filling is as dry as possible is crucial for achieving crisp egg rolls.

Once fully drained, transfer the vegetables into a spacious mixing bowl. Add the scallions, salt, sugar, white pepper, five-spice powder (if using), sesame oil, and two tablespoons of your chosen cooking oil. Incorporate the roast pork and shrimp (if included), then mix thoroughly until the filling is evenly combined.

To assemble the egg rolls, take a small handful of the filling and press it gently to compact. Position it on an egg roll wrapper, folding and rolling in a manner similar to wrapping a burrito. Apply a thin layer of beaten egg to the edges to seal. Arrange the assembled egg rolls on a lightly floured surface, repeating the process until all ingredients have been utilized.

In a deep, small pot, heat the oil to 325°F (160°C). Use enough oil to fully submerge the egg rolls. Carefully lower a few egg rolls into the hot oil, ensuring not to overcrowd the pot. Fry for approximately 5 minutes, turning occasionally to promote even browning, until they achieve a golden, crisp exterior.

Remove the egg rolls from the oil and allow them to cool slightly before serving. Store any leftovers in freezer-safe bags and reheat in a preheated oven at 350°F (175°C) until crisp.