Step 1

Khao Soi Paste: Place chiles in a small heatproof bowl, add boiling water to cover, and let soak until softened, 25–30 minutes.

Step 2

Drain chiles, reserving soaking liquid. Purée chiles, shallots, garlic, ginger, cilantro stems, coriander, turmeric, curry powder, and 2 Tbsp. soaking liquid in a food processor, adding more soaking liquid by tablespoonfuls, if needed, until smooth.

Step 3

Soup: Heat oil in a large heavy pot over medium heat. Add khao soi paste; cook, stirring constantly, until slightly darkened, 4–6 minutes. Add coconut milk and broth. Bring to a boil; add chicken. Reduce heat and simmer until chicken is fork-tender, 20–25 minutes. Transfer chicken to a plate. Let cool slightly; shred meat.

Step 4

Meanwhile, cook noodles according to package directions.

Step 5

Add chicken, 3 Tbsp. fish sauce, and sugar to soup. Season with salt or more fish sauce, if needed. Divide soup and noodles among bowls and serve with toppings.