This is hands-down my favorite noodle dish to eat and cook. It comes from my mom's home region of northern Thailand. This dish is very reminiscent of the popular Japanese tonkotsu ramen. The coconut curry is fortified with a very rich broth. "Khao" is the Thai word for rice—in this case rice noodles—and soi means "to cut." So this dish was originally made with hand-sliced rice noodle sheets, but the modern version is adapted for thin wheat noodles.
In a medium saucepan, heat 3 tablespoons of the rich coconut milk (the white, opaque part that has risen to the top) to medium heat and stir in the curry pastes. Stir-fry this mixture for about 1 minute, until the paste starts to deepen in color and is thick and fragrant. Stir in the remaining coconut milk and lime leaves. Add the cooked chicken pieces and stir to coat the pieces in the paste, about 1 minute. Increase the heat to high to bring to a boil. Allow this to boil for about 5 minutes, then reduce the heat to a strong simmer, about 10 minutes. Once the volume of liquid has evaporated by about 1/4 or the liquid coats the back of a wooden spoon, proceed.
Next, add the fish sauce, sugar and tamarind. Finish with the chicken stock. Taste and adjust as necessary.
To serve: Separate the noodles into 4 bowls and place a chicken leg in each. Ladle about 6 to 8 ounces of the rich broth over each noodle bowl. Garnish with crispy noodles, mustard greens, shallots, scallions and cilantro on top.
Thai Chicken Stock:
Place the chicken leg quarters in a stock pot and cover with 8 cups cold water. Bring to a simmer. Add the galangal, lemongrass, lime leaves, garlic, shallot and chiles to the stock and allow to simmer. Skim foam and fat often, continue to simmer for about 1 hour 30 minutes. Reserve the cooked chicken legs. Skim off any additional fat and strain the stock through cheesecloth.
Reprinted with permission from 101 Asian Dishes You Need to Cook Before You Die by Jet Tila, Page Street Publishing Co. 2017.