Clean the taro stem, herbs, and tomatoes. Blanch the pork ribs in boiling water, then rinse. Simmer the ribs in 2 quarts (about 2 liters) of water until tender, skimming off any foam.

Once the ribs are tender, season the broth to taste. Add the tomatoes, shrimp, and mushrooms. Just before serving, add the taro stem. Place rice vermicelli noodles in bowls, top with ribs, shrimp, and pork sausage. Ladle the broth over, then garnish with Vietnamese coriander, cilantro, scallions, and fried shallots. Serve with thinly sliced lettuce on the side.