Soak the dried rice noodles in cool or lukewarm water for 40 minutes to an hour, or until limp but still firm to the touch. While the noodles are soaking, mix the fish sauce with the tamarind juice and palm sugar; stir well to melt the sugar. Taste and adjust flavors to the desired combination of salty, sour and sweet. Prepare the remaining ingredients as instructed.
When the noodles have softened, drain and set aside. Heat a wok over high heat until it is smoking hot. Add 2 tsp. of oil and quickly stir-fry the prawns until they turn pink and are almost cooked through. Salt lightly with a sprinkling of fish sauce and remove them from the wok.
Swirl in the remaining oil, save for 1 teaspoon, to coat the wok surface and wait 20 to 30 seconds for it to heat. Add the tofu, frying 1 to 2 minutes, or until the pieces turn golden. Add garlic and stir-fry with the tofu for 15 to 20 seconds. Follow with the sliced shallots and cook another 15 seconds. Then add the dried shrimp, sweetened salted radish and ground dried chillies. Stir and heat through for a few seconds.
Add the noodles and toss well with the ingredients in the wok. Stir-fry 1 to 2 minutes and when most of the noodles have changed texture and softened, push the mass up along one side of the wok. Add the teaspoon of oil to the cleared area, crack the eggs onto it and scramble lightly. When the eggs have set, cut into small chunks with the spatula and toss them in with the noodles.
Add the sweet-and-sour seasoning mixture. Stir well to evenly coat noodles. If the noodles are still too firm, sprinkle 1 to 2 tbsp. of water over them to help cook. Taste and adjust flavors as needed by adding more fish sauce or tamarind juice; if the noodles are not sweet enough, sprinkle in a small amount of granulated sugar.
When the noodles are cooked, toss in 2 of the 3 cups of bean sprouts and the garlic chives (if using). Sprinkle with half the chopped peanuts and return the prawns to the wok. Stir and when the vegetables are partially cooked, transfer to a serving platter, or dish onto individual serving-size plates, and garnish with the remaining bean sprouts and chopped peanuts, the lime wedges, cilantro and green onions.
Serves 4 as a one-dish lunch. Squeeze lime juice over each portion before eating.