Make the filling: In a large bowl, combine the ground pork, shrimp, ginger, soy sauce, white pepper, salt, and sesame oil. Mix in one direction until the mixture becomes sticky and binds together.
Add the vegetables: Fold in the green onion, shredded carrot, and corn. Keep the filling chilled while preparing the cabbage.
Prepare the cabbage: Cut off the bottom third of a Napa cabbage and separate the leaves. Wash thoroughly. For more pliable leaves, blanch them in boiling water with ½ tbsp salt for 30–60 seconds, then shock in cold water. Drain well.
Wrap the rolls: Place a spoonful of filling at the base of each cabbage leaf. Roll once to cover the filling, fold in the sides, and continue rolling tightly, just like a spring roll. You should get about 12–15 rolls.
Steam: Arrange the rolls on a plate in a single layer (or two at most). Steam over medium-high heat for about 10 minutes, then save the steaming liquid for the sauce.
Make the sauce: Heat oil in a small pan and sauté garlic until fragrant and lightly golden. Add soy sauce and oyster sauce. Mix cornstarch with the reserved steaming liquid (or water) and pour it in. Stir until the sauce thickens.
Finish & serve: Pour the sauce over the cabbage rolls. Garnish with chopped green onion or sliced Thai chili for a bit of heat. For an extra touch, drizzle with hot neutral oil to sizzle the sauce before serving.