Heat a frying pan on low heat, toss in the uncooked Thai sticky rice, no oil and stir continuously. Toast the rice until it turns from white to golden yellow, It will also be very fragrant and smell almost like popcorn. It took me about 15 minutes or so.
Once the rice is finished toasting, and has cooled off a bit, put it into your mortar and pestle and pound the rice until it turns into a coarse powder. Or use a blender. Set aside until serving. Place noodles in a medium heatproof bowl. Add boiling water to cover and let stand, stirring frequently, until soft and pliable but not tender, 5–10 minutes.
Meanwhile, whisk fish sauce, tamarind concentrate, brown sugar, 2 tsp. chili-garlic sauce, and 1/4 cup hot water in another medium bowl. Heat oil in a wok over medium-high. Add beef, prawns and chilli and cook, stirring constantly, until prawns begin to turn pink, about 1 minute. Add the eggs and spring onion whites, fish sauce mixture, and reserved noodles.
Cook, stirring frequently, until sauce is mostly absorbed and noodles are well coated, about 3 minutes. Add scallion greens, 2 cups bean sprouts, and 1/4 cup peanuts and cook until heated through, about 1 minute more. Divide noodle mixture among plates. Top with cilantro, bean sprouts, and peanuts and serve with lime wedges. And sprinkle over the rice powder.