Thinly slice pork and toss with soy sauce, and sugar. Let rest while you prep other ingredients so the pork takes on flavor and caramelizes better.
In a saucepan, combine tonkotsu broth, smashed garlic, mirin, and sesame oil. Gently warm until steaming, then keep on low heat.
Boil noodles according to package directions until just al dente. Drain and briefly rinse with hot water to remove surface starch and prevent sticking. Set aside.
Heat a wok or skillet over high heat until very hot. Add neutral oil and sear pork in a single layer for 1–2 minutes per side until caramelized. Remove pork, then stir-fry onion, carrot, and cabbage for 2–3 minutes until crisp-tender. Return pork, add ginger and scallions, toss, and finish with a quick splash of soy if needed.
Divide noodles among bowls, ladle hot tonkotsu broth over them, then top with wok-seared pork and vegetables. Add halved soft-boiled eggs, sprinkle sesame seeds, drizzle chili oil, and garnish with nori and scallions.
Notes
For true tonkotsu depth, use homemade broth if available; store-bought concentrates are an excellent shortcut.
Avoid overcrowding the pan when searing to get good caramelization.
Toss noodles with a little sesame oil if not serving immediately to prevent sogginess.