Place the ground crab in a pot with about 10 1/2 cups water (2.5 liters). Stir well, then strain through a fine mesh to remove the shells. Bring the crab broth to a simmer over low heat. Add a little vinegar or tamarind juice to help the crab form large floating curds. Skim off the crab curds and set aside in a bowl. Mix the crab curds with ground pork, pounded dried shrimp, duck egg, a splash of fish sauce, a pinch of MSG, sugar, pepper, minced shallots, and 2 tablespoons vegetable oil. Mix well.

Wash and prepare the fresh herbs. Blanch the rice vermicelli noodles briefly in boiling water. To serve, place noodles in a bowl, add a piece of steamed crab cake, pork sausage, and ladle hot broth over. Top with scallions, cilantro, and pepper for aroma.