KHAO SOI PASTE
4 large dried New Mexico or guajillo chiles, stemmed, halved, seeded
2 medium shallots, halved
8 cloves garlic cloves
1 2" piece ginger, peeled, sliced
¼ cup chopped cilantro stems
1 tablespoon ground coriander
1 tablespoon ground turmeric
1 teaspoon curry powder
SOUP
2 tablespoons vegetable oil
2 14-oz. cans unsweetened coconut milk
2 cups low-sodium chicken broth
1½ lb skinless, boneless chicken thighs, halved lengthwise
1 lb Chinese egg noodles
3 tablespoons (or more) fish sauce (such as nam pla or nuoc nam)
1 tablespoon (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)