Place beef bones and chuck into a large stockpot and cover with cold water. Bring to a boil, then immediately drain and rinse the bones and meat under cold running water to remove impurities, clean the pot, and return the blanched bones and meat to the pot with fresh water.

Heat a dry skillet over medium-high heat and char the onion halves cut-side down until deeply browned, about 5 minutes per side. Add the charred onions, smashed garlic, and crushed ginger to the stockpot.

Add kombu, dried shiitake mushrooms, and carrot chunks to the pot, bring to a boil, then reduce heat to low to maintain a gentle simmer.

Simmer the broth uncovered for 4 to 5 hours, skimming any foam that rises to the surface during the first 30 minutes.

Set a fine-mesh strainer over a clean pot and carefully strain the broth to remove all solids, discarding the bones and vegetables.

In a small saucepan over medium heat, combine soy sauce, mirin, and sake and warm until combined, about 2 minutes, to make the tare.

Bring a large pot of salted water to a rolling boil and cook ramen noodles for 3 to 4 minutes, then drain and rinse under cool water.

Prepare toppings: halve soft-boiled eggs, sauté shiitake mushrooms, slice green onions, blanch bean sprouts, slice chashu pork, and cut nori into strips. Warm ramen bowls with hot broth.

Divide noodles among bowls, pour in hot broth, arrange toppings (eggs, mushrooms, green onions, bean sprouts, pork, nori), drizzle with sesame oil, and finish with salt and white pepper.