In a well-supported granite mortar, first make the yellow kroeung (spice paste) by pounding the lemongrass with the pestle until you can no longer see the rings of the lemongrass and it's all mashed up.
Gradually add each of the galangal, turmeric, finger-root, kaffir lime leaves and zest and pound until they're incorporated into the mashed lemongrass.
Add the garlic and pound, then add the shallots and pound, until the paste is smooth, but still has some fibres from the lemongrass. Transfer the kroeung to a well-sealed container to refrigerate.
In a medium-sized pot or pan, poach the fish fillets with the prahok (mash and strain, ensuring there are no bones) or 2 tablespoons of fish sauce, palm sugar, and enough water to cover the fish, until the fish is cooked.
If the fish is soft enough, mash it in the pot with 4 tablespoons of kroeung and the juices. Alternatively, remove the fish fillets (leave the juices), transfer them to the mortar, and pound the fish with the kroeung until well combined.
Transfer the pounded fish-kroeung mixture to a medium-sized soup pot if you poached the fish in a pan, then add the coconut milk/cream, another tablespoon of fish sauce, and taste, adding more fish sauce or salt or palm sugar if needed, so that it’s balanced. Bring to a gentle boil then turn the heat down to low to simmer for 5-10 minutes, adding a little water if desired.
If you don’t have access to fresh rice noodles, prepare the dried rice vermicelli according to the instructions on the pack, drain and set aside to cool.
Bring the fish gravy to a gentle boil then turn the heat down to low to simmer for 5-10 minutes, adding a little water if desired if it reduces too much. When it’s ready, turn the heat off as it should be served warm to room temperature, but not hot.
If you don’t have access to fresh rice noodles, prepare the dried rice vermicelli according to the instructions on the pack, drain and set aside to cool.
Prep the vegetables, herbs and flowers while the rice noodles are cooling, then distribute them amongst the bowls, first placing the shredded banana blossom in the bottom of the bowl and then the rice noodles on top of these to diminish browning.
Ladle the fragrant fish gravy over the rice noodles, distributing evenly amongst the bowls, then arrange the bean sprouts, cucumber, water lily stems, and wing beans on top of the noodles.
Garnish each bowl with lime quarters, some edible flowers and chi (fresh herbs), and provide additional flowers and herbs in a basket at the centre of the table, along with condiments such as chilli flakes, chilli sauce and fish sauce.
Serve with a spoon and chopsticks and advise your guests if eating nom banh chok for the first time to use the chopsticks to combine the noodles, vegetables and garnish, and then taste before adding more garnish and condiments.