I first had this dish in Chiang Mai and loved it. The version we had in Chiang Rai is a little different, not a thick as the Chiang Mai version but still very tasty.
Khao Soi is a curry noodle dish from the northern part of Thailand. It is often made with chicken, served over Chinese Bah-mi egg noodle, and garnished with fried noodles, shallots, corriander, pickled mustard greens, fried whole chillis and a squeeze of lime juice.
Into a hot heavy bottomed pot, add the oil and the red curry paste, curry powder, cardamon and turmeric and cook, stirring vigorously, for a few minutes until the curry paste is fragrant. Be careful not to burn the paste.
Add a third of the coconut milk, stir to blend and let the pan come back to a boil. Let it bubble for a few minutes over high heat, stirring often, until you see the red oil separating from the coconut milk mixture. Add another third of coconut milk, again wait until the oil separates.
Add the chicken pieces to the pan, with the cup stock and the rest of the coconut milk. Let the pan come back to a boil, then lower the heat to simmer.
Add the fish sauce and sugar. Close the lid and let it simmer until the chicken is cooked. Check the seasonings, you might need to add more fish sauce. The flavor of the curry should be salty, spicy, and with a very slight after taste of sweetness.
Take 1 cup of the noodle, fluff up until the strands are separated. Fry a little bit at a time in a pan with very hot oil until golden, you will need to flip to noodle once in the pan to get the same color on both sides. Set aside
Use the oil to fry up the dried chilli, very quickly, be careful not to let them burn. Set aside.
Slice the shallots, rinse and slice the mustard greens, cut up the limes, chop the cilantro. Set aside.
After the chicken curry is done, heat up a large pot of water to a full boil. Rinse the rest of the fresh noodles first in cold water to wash out the excess starch, then cook in the very hot boiling water for 2-3 minutes. Stir the noodles well to prevent sticking.
Put some cooked noodles in a bowl, top with the curry, and the garnish to taste. Squeeze some lime juice into the bowl just before eating. You could add the dried chillies if you want more heat.