Char the outside of one Onions and a thumb-sized piece of Fresh ginger directly over a gas flame or under a broiler until blackened, then peel off any loose burnt skin and set aside.
Toast the whole spices in a dry skillet over medium heat until fragrant — Star anise, a Cassia cinnamon stick, Coriander seeds, Whole cloves and a Black cardamom pod — then lightly crush the coriander and cardamom to release their oils.
In a large stockpot, place the rinsed Whole chicken and cover with cold Water. Bring to a rolling boil, then reduce to a gentle simmer and skim off any foam and impurities with a ladle.
Add the charred Onions and Fresh ginger, the toasted spices, a small piece of Yellow rock sugar, and season with Fish sauce and Fine sea salt. Simmer gently, partially covered, for 45–90 minutes until the chicken is cooked through and the broth is aromatic and clear.
Carefully remove the chicken from the pot and set aside to cool slightly. Strain the broth through a fine-mesh sieve or cheesecloth into another pot, discarding solids, and skim or refrigerate briefly to remove excess fat if desired. Taste and adjust seasoning with more Fish sauce or Fine sea salt if needed.
Prepare the Dried flat rice noodles (bánh phở) according to package instructions — typically by soaking in hot water or briefly blanching in boiling water — until tender but still springy, then drain and portion into serving bowls.
Shred the cooled Whole chicken into bite-sized pieces, discarding the bones and skin as you prefer.
Thinly slice the White onion, chop the Scallions, roughly chop the Cilantro and Sawtooth herb (ngò gai), and thinly slice the Bird’s eye chilies. Cut the Limes into wedges for serving.
To assemble: place a nest of noodles in each bowl, top with shredded chicken, and ladle the steaming hot broth over to heat everything through. Garnish with sliced White onion, Scallions, Cilantro, Sawtooth herb (ngò gai) and Bird’s eye chilies; serve with Limes to squeeze at the table.
Serve immediately so the herbs stay bright and the broth is piping hot; offer extra Fish sauce or chiles for guests to adjust seasoning and heat to taste.
