Cut off the roots of coriander and scallion. Set the roots and some lime leaves aside. Finely chop coriander, fresh chili, scallion, and the remaining lime leaves.
Halve the shallots. Cut the lime into wedges. Score the husk of the sugarcane stalks, then chop them into thin sticks.
Bake onions, shallots, and ginger in the oven for 15 minutes.
Add chicken to the stock pot with 4 liters of water, the baked ingredients, and 2 teaspoons of salt. Simmer the chicken on medium heat for 30 - 40 minutes.
Constantly skim off the foam during the process.
In a skillet, roast fennel, coriander seeds, allspice, cloves, dried onions, black cardamom, cinnamon sticks, star anise, dried ginger, coriander roots, and scallion roots on high heat until fragrant.
When the mixture cools down, stuff it into a filter bag.
Remove the cooked chicken from the pot. Add the spice bags and sugarcane sticks to the pot.
Continue to add lime leaves, brown rock sugar, and salt to the pot. Simmer on low heat.
Peel the meat off the chicken and cut the flesh into bite-sized pieces, but keep the wings and drumsticks intact.
Move the chicken bones to the simmering pot, plus some seasoning to taste.
Cook on low heat for 10 - 15 minutes.
Parboil Phở noodles in hot water for 15 - 20 seconds. Add some vegetable oil to the water to keep the strands from sticking to each other.
Put the noodles and chicken slices in a bowl. Pour the broth and drizzle chopped aromatic herbs on top. Serve with your favorite sauces and toppings.