01 - Place chicken, onion, ginger, and water in a large stockpot. Bring to a boil over high heat, then reduce to a gentle simmer. Skim off any foam that rises to the surface. After 30 minutes of simmering, carefully remove the chicken and set aside to cool.
02 - Continue simmering the broth with onion and ginger for another 45 minutes to develop depth. Add salt, fish sauce, and sugar. Strain the broth through a fine mesh strainer for clarity and return to the pot. Keep warm.
03 - Once the cooled chicken is comfortable to handle, shred the breast meat into thin strips. Reserve for serving. The remaining chicken can be saved for another use.
04 - Whisk eggs with 1/4 teaspoon salt. Heat a nonstick skillet over medium-low heat. Pour a thin layer of egg to create a flat crepe. Cook until just set, flip briefly, then remove. Repeat until all egg is used. Slice crepes into fine julienne strips.
05 - Prepare rice vermicelli according to package instructions. Rinse thoroughly with cold water to stop cooking and prevent sticking. Drain well.
06 - Cut Vietnamese pork sausage into thin julienne strips, matching the texture of other toppings.
07 - Divide noodles evenly among serving bowls. Arrange shredded chicken, egg crepe strips, and pork sausage on top. Scatter scallions, cilantro, Vietnamese coriander, mint, and chili over each bowl.
08 - Ladle the hot, clear broth over the arranged toppings. Garnish with shrimp floss and lime wedges. Serve immediately with shrimp paste on the side for those who enjoy it.