For the Meatballs:
- Make the chicken and prawn mixture: Roughly chop the garlic, shallots, red chilies, Prik Kee Nu green chilies (if using), and coriander roots. Using a mortar and pestle, pound into a coarse paste. Mince half of the prawns into a paste, and coarsely chop the other half. Transfer the garlic chili paste to a large mixing bowl, and add the minced and cubed prawns, ground chicken, ground white pepper, fish sauce, low sodium light soy sauce, and sesame oil. Mix until combined well. Scoop the meat mixture up with a large spoon and drop it so that it slaps against the bowl. (Note: You can also combine the meat using your hands instead, which is the traditional way.) Repeat a few times until the texture becomes smooth and everything has come together. Set aside.
For the Thai Glass Noodle Soup:
- Prepare the ingredients: Roughly chop the garlic and red chilies, then pound into a coarse paste using a mortar and pestle. Thinly slice the shallots, and finely mince the lemongrass and kaffir lime leaves. Soak the mung bean vermicelli in a bowl with room temperature water as per package instructions, then drain well. Cut the noodles with kitchen shears into more manageable lengths (so that they are easier to eat).
- Make the soup: Heat the canola oil in a large stockpot of Dutch oven over medium-high heat. Once hot, add the shallots and sauté for 30 seconds until slightly softened. Then add the garlic chili paste mixture, lemongrass, kaffir lime leaves and sauté for a minute until fragrant. Pour in the water and season with fish sauce, low sodium light soy sauce, ground white pepper, kosher salt, and Thai chili powder (if using). Once the water starts to boil, turn the heat down to medium. Use a teaspoon to scoop up the chicken and shrimp meat mixture, and another to slide it off the spoon and into the soup. Repeat until all of the meatballs are in the soup. Simmer for 2-3 minutes, or until the meatballs are just cooked. Give the broth a taste and adjust seasoning by adding more fish sauce, soy sauce, or kosher salt if needed. When you are ready to serve, add the noodles and stir in the chopped coriander and spring onion. Then switch off the heat.
- To Serve: Divide the noodle soup and meatballs evenly into bowls. Briefly blanch Asian greens of your choice and add to the bowls. Serve with fried shallots and Chinese chili oil if desired.