Soak the preserved mustard greens in warm water for 10 minutes, then rinse 2–3 times and wring out all the water. Simultaneously, place the whole pork belly in a pot with water, 2 slices of ginger, and about 1 tbsp of cooking wine; bring to a boil and simmer for 8–10 minutes (no pressure). Remove the pork, pat dry the surface thoroughly with paper towels, especially the skin.