01 - In a large pot, add chicken, onion, ginger, and water. Bring to a boil, then reduce heat and simmer, skimming off any foam. After 30 minutes, remove the chicken and set aside to cool.
02 - Continue simmering the broth with the onion and ginger for another 45 minutes. Add salt, fish sauce, and sugar. Strain the broth for clarity and return to the pot.
03 - Shred the cooled chicken breast into thin strips. Reserve for serving.
04 - Whisk eggs with 1/4 tsp salt. Heat a nonstick skillet over medium-low. Pour a thin layer of egg to make a flat crepe. Cook until just set, flip, then remove. Repeat as necessary. Slice crepes into fine julienne strips.
05 - Cook rice vermicelli according to package instructions. Rinse with cold water and drain well.
06 - Slice Vietnamese pork sausage into thin julienne strips.
07 - Divide noodles among bowls. Top with shredded chicken, egg crepe strips, pork sausage, scallions, cilantro, Vietnamese coriander, mint, and chili.
08 - Ladle the hot, clear broth over the toppings. Garnish with shrimp floss and lime wedges. Serve with shrimp paste on the side, if desired.