Step 1: Make the filling. If using dried shiitake, cover with boiling water and leave for 20 minutes until soft, then drain and squeeze out excess water before chopping finely. Put the napa cabbage in a bowl with a pinch of salt, leave for 5 minutes, then squeeze firmly to remove as much water as possible - this prevents a soggy bottom layer. Combine the ground pork, cabbage, mushrooms, scallions, garlic, ginger, soy sauce, oyster sauce, sesame oil, rice wine vinegar, sugar, white pepper, and salt in a large bowl. Mix with your hands until the mixture is combined and slightly sticky. The texture should be cohesive rather than loose.

Step 2: Set up your steaming situation. You need a deep heatproof dish roughly 7x9 inches and at least 3 inches deep - a deep baking dish, a Dutch oven, or a large cake pan all work. You'll be steaming this on the stovetop: place the dish inside a large pot or wok with enough water to come about 1 inch up the sides of the dish. Get the water simmering before you assemble so it's ready to go.

Step 3: Layer the lasagna. Spread a thin layer of the pork filling across the bottom of the dish - about a third of the mixture. Lay dumpling wrappers over the filling with minimal overlap, covering it completely like lasagna sheets. Spread another third of the pork mixture over the wrappers, pressing it down gently. Add another wrapper layer. Finish with the remaining pork mixture, then a final layer of wrappers on top. Pour 4 tablespoons of water evenly over the top wrapper layer.

Step 4: Steam. Cover the dish tightly with foil or a lid. Place in the pot over the simmering water, cover the pot with its own lid, and steam over medium heat for 25-30 minutes. The pork should be completely cooked through and the wrappers soft and slightly translucent. Check by pressing the top layer - it should feel firm rather than springy, and the edges should have pulled away slightly from the sides of the dish.

Step 5: Make the ginger scallion oil. While the lasagna steams, put the finely sliced scallions and grated ginger in a small heatproof bowl with a pinch of salt. Heat the sesame oil in a small pan until it just begins to smoke. Pour it directly over the scallion and ginger mixture - it will sizzle immediately and bloom the aromatics. Stir and set aside.

Step 6: Finish and serve. Remove the foil carefully - steam will escape. Drizzle the chili crisp and soy sauce over the top. Spoon the ginger scallion oil across the surface. Scatter over extra sliced scallions and sesame seeds. Serve immediately, cutting through all the layers and making sure to get some of the liquid from the bottom of the dish into every bowl. Serve with steamed rice.