Begin by adding your chicken pieces, skin side up, to a slow cooker. Season with salt and pepper, and add 2 cups of the chicken stock. Cook on high for 4 hours, then remove the chicken. Reserve the stock.
I poured my stock into my OXO fat seperator, and let me just say, I love this thing. It allows you to quickly strain any bits, and allows for a clean pour of enriched stock, removing any of the fat. So pour the stock into your soup pot, along with the additional 2 cups of stock, and set it aside.
Remove the skin from the chicken and discard. Pull the chicken apart with a couple of forks. It should be super tender. Add the chicken to the stock, and bring that up to medium heat.
Slice your mushrooms in half, vertically.
Add the mushrooms, coconut milk, Thai chilies, lemongrass, and galangal into the pot. Give a good stir, and let that come to a simmer.
Once simmering, lower the heat, and let the ingredients infuse the stock, cooking for about 45 minutes. After 45 minutes, toss in the lime juice, and fish sauce. Stir, and cook another 5 minutes or so.
To serve, add some of the cooked rice into your soup bowl, and ladle in a generous amount of the soup, keeping all ingredients together. Inform your guest that they should not eat the lemongrass, kaffir, nor galangal. Those are really only there for flavor. Toss in some basil, and dig in.