In a wok set over moderately high heat heat the oil until hot. Add the ginger, onion and celery and stir-fry 1 minute. Add the cabbage and bean sprouts and stir fry 2 to 3 minutes more, or until vegetables are slightly softened. Add the pork and shrimp and stir-fry 1 minute more. Add the chicken stock and sugar, bring the mixture to a boil and stir in the cornstarch mixture. Simmer until lightly thickened. Stir in sesame oil, salt and pepper to taste.
In a saucepan have water at a boil. Remove from heat and whisk in cornstarch mixture. Have ready 12 egg roll wrappers under dampened towel. Place a portion of the filing in a line diagonally across one corner of wrapper, brush with some of cornstarch paste and fold in the ends. Roll tightly to make a sealed cylinder. Repeat with remaining wrappers. Have oil heated to 350 degrees F. Fry egg rolls, in small batches, turning, for about 4 minutes, or until golden brown. Transfer to paper towels to drain. Makes 12 egg rolls.