Place the chicken in the stockpot and cover with water. Bring to a boil over medium-high heat, then reduce to a simmer and cook until tender, about 15 minutes. Remove chicken, let cool slightly, then shred using forks or your hands.
While the chicken cooks, thinly slice the ginger and bruise the lemongrass stalks with the side of your knife to release their aroma.
Heat oil in the same stockpot over medium heat. Add sliced ginger and bruised lemongrass, sauté until fragrant and slightly golden, about 2 minutes, releasing a spicy aroma.
Pour in the chicken broth and bring to a gentle simmer, allowing the flavors to meld for about 10 minutes. Skim off any foam or impurities that rise to the surface.
Add sliced carrots and celery to the broth, cooking for about 5 minutes until they start to soften but remain crisp.
Stir in the shredded chicken, fish sauce, and season with salt and pepper to taste. Let the soup simmer gently for another 10 minutes, allowing flavors to deepen and vegetables to become tender.
Taste the broth and adjust seasoning as needed—adding more fish sauce, salt, or pepper for your preferred flavor balance.
Remove the lemongrass stalks and ginger slices if desired, or leave them for extra flavor.
Ladle the hot soup into bowls, then garnish with chopped scallions and cilantro for a fresh, vibrant finish.
Serve immediately with a side of rice or enjoy on its own for a nourishing, zesty meal that’s both bright and comforting.
