Pat the beef cubes completely dry with paper towels, then blanch them in a large pot of boiling water for 3 to 4 minutes to remove impurities and excess blood; drain and rinse under cold water.

Heat 2 tablespoons of vegetable oil in a large pot over medium-high heat until shimmering, then add the crushed garlic, ginger slices, and quartered onion and cook for 3 to 4 minutes until fragrant and lightly charred.

Add the dried chilies, star anise, cinnamon stick, bay leaves, and Sichuan peppercorns to the pot and stir for 1 to 2 minutes until the spices release their oils.

Stir in 3 tablespoons of doubanjiang and cook for 1 to 2 minutes, breaking up any lumps.

Return the blanched beef to the pot, pour in 8 cups of beef stock and 4 cups of water, and bring to a boil over high heat; skim any foam that forms.

Add 2 tablespoons of soy sauce, 1 tablespoon of dark soy sauce, and 1 tablespoon of rock sugar, then reduce heat to low, partially cover, and simmer gently for 1 hour 30 minutes to 2 hours until beef is tender.

Taste the broth after 1 hour 30 minutes and adjust seasoning with salt, white pepper, and additional chili to taste.

Meanwhile, bring a separate pot of salted water to a boil and cook the noodles according to package instructions (2-3 minutes for fresh, 4-5 minutes for dried), then drain.

Divide the cooked noodles among bowls, ladle the hot beef and broth over them, drizzle with sesame oil, and top with green onions, cilantro, and chili oil as desired.