In the large pot, bring water to boil. Make sure you have enough water to cover the vermicelli. Once it boiled, cook noodle for 7-8 minutes or until the noodle cook to your liking. Rinse noodle under running cold water. Set aside.
Thinly slice 4 cloves of shallot, add oil in the pan and sautee until light brown.
Wash tomatoes and cut them into quarter slices, add to the pan and stir fry 3-4 minutes until slightly soften.
In the large pot, add water and pork ribs. Cook it for about 20 minutes. Occasionally, remove dirty bubbles. Continue to add shallots, tomatoes, rock sugar, 3 tbsp fish sauce, ketchup. Turn down to medium low heat, continue to cook for another 20 minutes.
While waiting for the soup base, we will make gach cua (meatball). Add shallots into a small food processor, pulse until finely chopped.
Peeled the shrimp, continue to add to the food processor, pulse 4-5 times. Put it in a large bowl
Continue to add crab meat, ground pork, eggs, 1 tbsp fish sauce, pepper. Mix until well combined.
Raise the heat, using a spoon to scoop meatball and slowly add to the soup. Repeat the steps until it's completed.
The last step, you will add tofu and fermented shrimp. Taste and adjust your flavor