Rinse the leaves
Pick through the Lá Giang Leaves, discard any tough stems or bruised bits, rinse them well under the tap, and let them drain. Give a few of the leaves a gentle scrunch between your fingers so they'll break down easily in the soup.
Prep the aromatics
Peel and thinly slice the Shallots, mince the Garlic, and bruise the Lemongrass with the flat side of your knife before cutting it into 5 cm pieces. Lightly crush the Bird's Eye Chilies, keeping the heat level where you want it.
Brown the chicken
Heat the Cooking Oil in a large pot over medium heat. Add the shallots and cook for 2 minutes until softened. Stir in the garlic, lemongrass, and chilies for 30 seconds until fragrant, then add the Chicken pieces and cook, turning them, until the outside is opaque and lightly golden, about 5 minutes.
Simmer the soup
Pour in the Water, then stir in the Fish Sauce, Salt, and Sugar, scraping up any browned bits from the bottom of the pot. Bring the soup to a boil, then lower it to a gentle simmer and cook for 20 minutes. Add the leaves and simmer for 5 minutes more, until they're wilted and the broth tastes pleasantly tart.
Finish and serve
Taste the broth and adjust with a little more fish sauce, salt, or sugar if needed. Rinse and dry the Scallion, thinly slice it, and chop the Rice Paddy Herb, then ladle the soup into bowls and scatter the herbs over the top.
