Add 2.5 L of water to a large pot and bring it to the boil on high heat. Once the water is boiling, add the chicken (breast side down) and bring it back to the boil. Remove the scum off the surface with a spoon.
Add all the soup base ingredients, except the fish sauce. Let it come back to the boil, then partially cover the pot with the lid and allow the soup to simmer for 50 minutes on medium low.
During the simmering phase, remove the scum/fat build up on the surface of the soup with a spoon. I personally do not remove all the fat from the soup, as I prefer to leave a bit for flavour.
Boil salted water and cook the pasta till al dente. Drain and set aside.
After 50 minutes turn off the heat and allow the chicken to sit in the soup for 10 minutes.
Remove the chicken from the pot and let it cool on a plate. Check the chicken is cooked though. If still raw, put it back into the soup until done.
Strain the soup with a strainer. Squeeze the liquid out of the veggies by pushing it against a strainer or keep whole and serve on the side.
Add 3 tbsp of fish sauce to the soup. Check the soup for seasoning and add more according to your taste. (Note 2)Note: Use fish sauce to up the salt content of the soup or boiling water to dilute the flavour.
Place the pasta into each bowl.
Shred pieces of chicken and place on top of the pasta.
Pour the boiling soup over the top of the pasta and chicken.
Sprinkle garnishes on top.
The best way to get coriander root is to buy coriander with roots attached. If this is not possible you can substitute with 2 tbsp of coriander seeds or just omit all together.
The soup should be slightly saltier then how you would normally have it. This is because the pasta and garnishes will dilute the flavour and seasoning.