Place the noodles in a large bowl and cover with boiling water. Let soak until softened, 10 to 15 minutes. Drain and toss with 1/2 teaspoon toasted sesame oil to prevent sticking.
In a small saucepan or wok, heat the beef stock to a simmer and then keep warm on low heat.
In a small frying pan set over medium heat, dry-toast the peppercorns until fragrant. Remove from the heat and crush in a mortar and pestle, place in a plastic bag and crush with a rolling pin or use a spice grinder.
Heat a wok over high heat and add the peanut oil. Add the garlic, ginger, chili and 1 tablespoon of the ground peppercorns and stir-fry a few seconds. Add the pork and chili bean sauce and continue stir-frying. As the pork browns, add the rice wine. When the pork has browned, add the tofu and mix gently. Season the stir-fry with soy sauce,
black rice vinegar, the remaining 1 teaspoon sesame oil, salt and ground white pepper.
Add the hot beef stock to the pork and tofu and bring to a boil. In a small bowl, stir together the cornstarch and 2 tablespoons water, then stir into the sauce to thicken. Stir in the scallions and remove from the heat. Serve over the noodles and sprinkle with the remaining peppercorns.