Cover the wood-ear mushrooms with hot water for several minutes to rehydate them. Then rinse, discard the tough stems, roll them together and julienne. Roughly chop the julienned mushrooms.
Place a pan over medium heat and add about 2 teaspoons of oil. Once the oil is hot, sauté minced shallots for a few seconds until fragrant. Then add garlic and ginger and cook for a few more seconds until fragrant.
Add the chopped wood-ear mushroom to the pan, stir and cook for about a minute. Add fish sauce, stir and cook for a few more seconds and then transfer to a mixing bowl to let it cool slightly.
Add ground pork, 1/4 teaspoon of salt and black pepper to the mixing bowl with the wood-ear mushroom. Mix together until just combined to make the filling for the cabbage rolls.
Heat plenty of water in a pot or deep pan. Once the water is simmering, add the cabbage leaves and blanch briefly just until they start to get softened. Transfer to a plate, then add scallion stalks to the water and also blanch briefly until just softened. Remove from the water.
On a clean working surface or cutting board, lay a cabbage leaf flat. Place 1 tablespoon to 1 1/2 tablespoon of filling on one end of the leaf and roll into a cabbage roll about 2 1/2 inch long. Use a long strip of scallion to wrap around the roll and tie a knot twice to secure the roll. Continue with the remaining leaves and filling.
Bring 2 1/2 to 3 cups of water to a boil. Add 1/2 teaspoon of salt and then add the cabbage rolls. Once it starts to boil again, lower the heat to maintain a simmer. Simmer for 10-12 minutes until the filling is fully cooked and the leaves are tender. You can taste the soup and adjust seasoning to taste.
Transfer the cabbage roll soup to individual serving bowls or a large serving bowl to share. You can sprinkle some black pepper on top and garnish with chopped cilantro.