Heat a medium sauté pan over medium-low heat. Add the chili peppers, garlic, shallots, lemongrass, ginger to the pan, stirring or shaking the pan occasionally to prevent it from burning.
After 2 minutes add the coriander, cumin and pepper to the pan, continuing to dry roast the ingredients until they darken, stirring constantly.
Remove from heat and let cool then add to the bowl of a food processor. Add the vegetable oil and pulse until the mixture is completely combined and forms a paste.
For the soup:
Heat a large heavy-bottomed pot or Dutch oven over medium heat, add vegetable oil and heat through. Add the khao soi paste, turmeric and curry powder and cook, stirring constantly so that the mixture does not burn, until the paste is fragrant, about 2 minutes.
Add 1 cup of the coconut milk and bring to a boil. Continue to boil, stirring, until red oil separates from the coconut mixture. Add an additional cup of the coconut milk and again boil until the oil separates.
Add the chicken, 2 cups of the chicken stock, lime leaves (optional) and the remaining coconut milk. Bring the mixture back to a boil then lower the heat to medium low and cover the pot and simmer, until the chicken is tender, about 45 minutes.
Stir in the soy sauce and fish sauce, continuing to simmer, uncovered, for an additional 15 minutes.
For serving:
Bring a large pot of water to the boil. Add ¾ of the noodles and cook, stirring occasionally, until al dente, about 10 minutes. Drain and return the noodles to the pot. Set aside until ready to serve.
In a heavy-bottomed saucepan or deep fryer add enough oil to fill 2-inches of the pan. Heat oil to 350ºF (180ºC). Fry the remaining noodles until golden brown, about 1 minute. Remove and drain on a paper towel-lined plate.
Divide the cooked noodles among soup bowls and add chicken to each bowl. Ladle the broth over the noodles and top with the fried noodles. Serve with red onion, cilantro leaves and lime wedges.