Rinse the pork bones thoroughly. Boil them briefly in enough water to cover, then discard the water to remove impurities. Rinse the bones with cold water, then simmer them in a pot with about 8-12 cups water (2-3 liters). Once boiling, reduce the heat and skim off any foam to keep the broth clear.

Place the ground crab in a large bowl. Add about 8 cups water (2 liters) and let it soak while you wash and cut the tomatoes into wedges. Peel and thinly slice the shallots, then fry them until golden and crispy.

Return to the crab mixture. Stir the water, then strain it through a fine mesh sieve to separate the crab solids. Repeat this process two more times, using less water each time. Add 1 tablespoon good-quality fish sauce to the strained crab liquid, then beat in 1 egg.

Bring the crab liquid to a boil. As it boils, the crab will float to the top. Skim off the crab mixture and set aside, then pour the liquid back into the pot.

Add the pork bone broth to the crab broth. Sauté garlic and tomatoes in annatto oil until fragrant, then add the fried tofu and tomatoes to the soup pot.

Season the broth with shrimp paste, fish sauce, salt, and sugar to taste. Simmer tamarind pods in a little water, then mash to extract the tamarind juice for serving. Blanch the rice vermicelli noodles, place them in bowls, ladle the broth over, top with the crab mixture, and serve with a little shrimp paste for extra flavor.