Heat a dry skillet over medium-high heat. Add the ginger slice and onion, charring them until the surface is blackened and fragrant. Set aside.
In a separate dry skillet over medium heat, toast the cinnamon stick, star anise, coriander seeds, fennel seeds, and cloves until they are aromatic (about 1–2 minutes). Stir occasionally to avoid burning.
In a medium-sized pot, combine the chicken, water, charred ginger, and onion. Add the toasted spices to a spice strainer or cheesecloth pouch and secure tightly. Place the strainer or pouch into the pot with the chicken and aromatics.
Bring the pot to a boil over high heat, then reduce the heat to low and let it simmer gently for 1 hour. During this time, skim off any foam or impurities that rise to the surface to ensure a clear broth.
After simmering, remove the chicken. Shred the meat and discard the skin and bones. Strain the broth to remove solids, then season with fish sauce, sugar, and salt to taste.
Cook rice noodles according to package instructions. Drain and rinse under cold water to prevent sticking. Place cooked noodles into a bowl. Add shredded chicken on top. Pour the hot broth over the noodles and chicken.
Add fresh herbs, bean sprouts, green and white onions, and chili slices. Serve with lime wedges and condiments like hoisin sauce or Sriracha on the side.
