Mix the crab meat, minced pork, eggs and 1 tbsp fish sauce thoroughly in a bowl.
Bring the stock to the boil, then over low heat, drop in the crab mixture by tablespoonfuls. Cook for 8-10 minutes, until the pieces float up and set.
Sauté the shallots in the oil in a pan, add the tomato, and cook for 5 minutes, until it starts to soften.
Pour the tomato into the soup, add the tamarind, sugar, remaining fish sauce and, if using, the shrimp paste. Cook for 10 minutes, season with salt; it should be tangy-salty-sweet.
Boil the rice noodles as directed on the packet, drain, and rinse with cold water.
Divide the noodles into bowls, top with the fried tofu, and pour over the hot soup with the crab pieces.
Serve with bean sprouts, fresh herbs and lime wedges.
A Receptnaptár original recipe. Calories and protein are estimated.
Tips
The traditional version is made with fresh freshwater crab; at home, tinned or frozen crab meat and prawns work well too.
Shrimp paste has a strong smell but gives deep flavour; start with less of it.