Add chicken and all broth ingredients into a pot, except the salt. Bring to a boil, then reduce to a simmer for ~15-20 minutes or until chicken is cooked through. Season to taste with salt. Discard onion.
Meanwhile, prepare the eggs. Beat eggs in a bowl and add 1-2 tablespoons water to thin it out a bit. Lightly oil a pan and add just enough egg to make a thin layer, flipping about midway. Make as many as it takes to use up all the eggs, then loosely roll the egg crepes individually to cut into strips / julienne.
Remove chicken from broth when it's fully cooked. Wait until cool, then shred. Cut the Vietnamese sausage to match the thickness of the chicken and eggs.
Lightly fry or deep-fry thinly sliced shallots if you want to use this.
Prepare rice noodles according to package instructions.
Assemble your soup bowls. Add noodles, toppings, herbs, garnish, broth, a few drops of beetle extract per bowl, and serve.