Place the ground crab in a pot with about 8 1/2 cups water (2 liters). Stir well, then strain through a fine mesh to remove solids. Bring the crab broth to a simmer over low heat. Add a splash of vinegar to help the crab set. Skim off the crab mixture and transfer to a bowl. Mix with ground pork, mashed dried shrimp paste, duck egg, a splash of fish sauce, a pinch of MSG, sugar, pepper, minced shallot, and 1 tablespoon cooking oil. Mix well, shape into patties, and steam until cooked through.

Rinse the apple snails in salted water, then clean thoroughly. Marinate the snails with minced shallot, fish sauce, salt, MSG, and pepper. Heat a pan with a little oil, sauté shallot until fragrant, then add the snails and stir-fry until cooked. In another pan, heat oil and sauté shallot, then add tomato wedges and cook until softened. Pour the tomatoes into the crab broth, add 1 tablespoon fermented shrimp paste, tamarind juice, fish sauce, sugar, and the white parts of green onions. Add the fried tofu and season to taste.

Blanch the rice vermicelli noodles and place in serving bowls. Top with steamed crab cakes, sautéed snails, and ladle hot broth over. Garnish with scallions, cilantro, and chili oil. Serve with fresh herbs.