Peel the whole onion and put in toaster oven to broil for around 6 minutes.
Wash the pork under running water and pat dry
Wash the shrimps and fresh crabs and drain. If using frozen crab meat, you should defrost in the refrigerator overnight.
Add the charred onion, daikon, onion, chicken powder, sugar, fish sauce and water in the Instant pot. Close the lid and set to High Pressure Cook for 10 minutes.
Meanwhile, boil the noodles according to package instructions. Make sure not to overcook! Drain and divide into 4 large bowls.
Wash and slice the green onion and coriander, set aside. Cut the lime into wedges
Mix well the tapioca starch and water to make a slurry or liquidy paste
When the Instant Pot pressure cook is done, manually release the steam and open the lid
Cancel the pressure cook function. Remove the pork and divide among the 4 bowls. and turn on the saute function
Add the crab paste, anatto oil (or red pepper powder).
When the broth is boiling, add the crab and shrimps. Boil until the crab shell turns orange and the shrimps turn opaque. This should be quite quick, especially if using crab meat instead of fresh crab. Remove the seafood and divide among the 4 bowls. Taste the broth and adjust seasoning (add sugar or fish sauce according to your taste). Fresh crabs add natural sweetness to the broth. If you use frozen or canned crab, you may want to add a little more sugar to the broth.
When the liquid boils again, add the tapioca starch/water slurry. Stir well to slightly thicken the broth.
Pour the piping hot broth over the bowls of noodles, pork and seafood. Sprinkle the green onions, coriander and crispy shallots (if used) on top. Serve with lime wedges and sliced Thai chili on the side.