Khao Soi Paste

4 large dried New Mexico or guajillo chiles, stemmed, halved, seeded
2 medium shallots, halved
8 garlic cloves
1 2-inch piece ginger, peeled, sliced
1/4 C. chopped cilantro stems
1 T. ground coriander
1 T. ground turmeric
1 tsp. curry powder

Soup

2 T. vegetable oil
2 14-ounce cans unsweetened coconut milk
2 C. low-sodium chicken broth
1 1/2 pounds skinless, boneless chicken thighs, halved lengthwise
1 pound Chinese egg noodles
3 T. (or more) fish sauce (such as nam pla or nuoc nam)
1 T. (packed) palm sugar or light brown sugar
Kosher salt
Sliced red onion, bean sprouts, cilantro sprigs, crispy fried onions or shallots, chili oil, and lime wedges (for serving)

Place chiles in a small heatproof bowl, add boiling water to cover, and let soak until softened, 25-30 minutes. Drain chiles, reserving soaking liquid. Purée chiles, shallots, garlic, ginger, cilantro stems, coriander, turmeric, curry powder, and 2 T. soaking liquid in a food processor (I used a Vita-Mix), adding more soaking liquid by tablespoonfuls, if needed (I needed about 6 T. total), until smooth. 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. Meanwhile, cook noodles according to package directions. Add chicken, 3 T. 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.