Special equipment: a piece of cheesecloth and some butcher's twine
For the broth: Heat a skillet over high heat. Add the ginger and cook, turning occasionally, until blackened and slightly charred, 2 to 3 minutes.
In a large stockpot, bring 8 cups water to a boil over high heat. Add the bouillon powder and stir to combine. Fold the cheesecloth into a square. Place the ginger, white and Sichuan peppercorns and star anise in the middle and tie the top with butcher's twine to make a pouch. Add the spice pouch to the broth. Stir in the bean sprouts, scallion whites and Napa cabbage stalks, bring to a boil, reduce to a simmer, and cook until the flavors have infused and the vegetables are tender, about 20 minutes. Strain the broth and keep warm.
Meanwhile, bring 5 quarts water and 1 tablespoon salt to a rolling boil. Stir in the noodles and cook until cooked through, 9 to 12 minutes, or according to package directions. Drain well.
Fry or steam the meatballs according to the package directions.
To serve, divide the noodles among 8 bowls. Ladle over the hot broth and top with the scallion greens, Napa cabbage leaves and meatballs. Serve with a drizzle of chili oil if desired.