Now it's time to make your broth. Add the onion that has been broiled and shrimp, the daikon, shrimp that have been dried, along with salt, to your pot. Pour in the water until it covers the entire ingredients. Bring the soup to a boil, then allow to simmer for approximately 45 minutes. While simmering, be sure you check the soup at least every 15 minutes, to remove any impurities.
While the soup is simmering cook your toppings. Bring your shrimp to a boil and then banh canh. Set aside.
After 45 minutes of simmering after which the meat will be cooked. Remove the meat from the bones, and then add the bones back into the pot. The meat is cut into pieces that are bite-sized and place aside.
Mix in the fish sauce, as well as chicken broth powder. Let it cook for 30 minutes.
While the broth simmers you can make the Annatto oil. Combine the annatto seeds and vegetable oils in a saucepan and let it simmer for about a minute until the oil begins to turn orange. Place the dish on a plate to cool.
Make a slurry of tapioca starch in 1/3 cup water. When the soup is finished simmering and thickening, add the tapioca slurry. The soup should simmer for 5 minutes until it begins to increase the thickness.
Then, add the oil of annatto, and then your soup is complete.