Preparation Gather half of cilantro into a bundle and tie together with kitchen twine. Coarsely chop remaining cilantro (stems and all); set aside for serving. Heat sugar and 3 Tbsp. water in a large saucepan over medium. Cook, stirring often, until sugar dissolves, about 2 minutes. Continue to cook, swirling pan occasionally, until syrup is golden amber, 4–6 minutes. Add ginger and cook, stirring occasionally, until ginger is softened slightly, about 5 minutes. Add garlic and pale-green and white scallion parts and cook, stirring often, until garlic is fragrant, about 2 minutes. Stir in cilantro bundle, chicken, chile, and a big pinch of salt. Pour in 8 cups cold water and bring to a boil. Reduce heat to medium-low, bring to a bare simmer, and cook, stirring occasionally, until chicken is cooked through, 10–12 minutes. Discard chile and scallions. Keep soup warm over medium-low heat. Transfer chicken to a plate and let cool slightly. Shred chicken and stir back into soup. Add soy sauce and stir to combine. Remove pot from heat; taste and season with salt, if needed. Serve soup topped with dark-green scallion parts, reserved chopped cilantro, and a few turns of pepper. Do Ahead Soup (without scallion greens or cilantro) can be made 3 days ahead. Let cool, then cover and chill.