Heat a wok, over medium-high heat. Drizzle in the oil and swirl around, then add the onion, ginger, garlic, and chili. Stir-fry 1-2 minutes to release the fragrance.
Add the stock plus the following: lemongrass, bay leaves, turmeric, chopped cashews, ground coriander, whole cumin seed, white pepper, cardamon, tamarind (or lime juice), shrimp paste, fish sauce, and sugar. Stir with each addition and bring to a light boil.
Add the chicken, stirring to coat with the spicy liquid, then add the coconut milk and potatoes. Stir and bring back up to a boil. Reduce heat to low, or just until you get a good simmer.
Simmer 30 to 40 minutes, stirring occasionally, until chicken and potatoes are tender. Add red pepper during last 10-15 minutes of coooking time.
Taste-test the curry, adding more fish sauce for increased flavor/saltiness, or more chili if you want it spicier. If too sour, add a little more sugar. If too salty or sweet for your taste, add a touch more tamarind or lime juice. If too spicy, add more coconut milk.
Add a handful more cashews and fold in. Transfer to a serving bowl, or plate up on individual plates or bowls. Top with fresh coriander, if desired, and serve with Thai jasmine rice. ENJOY!
Tamarind Substitution Tip: Tamarind paste can be tricky to find, hence I have offered a substitute here. Yes, lime and tamarind are two very different fruits; however, they provide that same sourness you're looking for in this curry (it is balanced out with the palm sugar or brown sugar). Whenever I run out of tamarind paste, I find lime juice works in a pinch. In fact, I have witnessed accomplished Thai chefs create tamarind-based dishes purely with lime juice (such as pad Thai) - good to know if you can't find tamarind paste where you live!
I buy my tamarind on line at Grocery Thai. I also buy Mussaman curry paste from there, makes this dish look a lot simpler when all the spices are already in the curry paste. I have substituted fresh peanuts pan roasted by me in place of the cashews.