Rinse the crabs thoroughly and soak them in salted water. Remove the shells. Blend the crab bodies with water until smooth. Strain to get clear crab broth, discarding the solids. Scoop out the crab roe from the shells and set aside.

Blanch the pork ribs in boiling water. Simmer to make broth until the ribs are tender.

Wash and cut the tomatoes into wedges. Heat annatto oil in a pan and sauté chopped shallots until fragrant. Add the tomatoes and crab roe, stir well. Season with fish sauce, sugar, salt, chicken bouillon, and MSG.

Simmer the strained crab broth over low heat. When it boils, crab paste will float to the top. Skim off the crab paste and set aside. Combine the crab broth and pork bone broth. Add the sautéed tomatoes to the pot.