Roast 1kg chicken bones at 200°C for 30 minutes. Transfer to a large pot with 3 litres of water, 1 halved onion, 4 garlic cloves, a thumb of ginger, and 2 tbsp soy sauce. Simmer for 3 hours, skimming regularly.
Combine 60ml soy sauce, 2 tbsp mirin, 1 tbsp sake (or dry sherry), and 1 tsp sesame oil in a small saucepan. Simmer for 5 minutes. Set aside.
Soft-boil 4 eggs for exactly 6.5 minutes, then cool in ice water. Slice 2 chicken breasts (poached or roasted). Slice 4 spring onions and prepare nori sheets and bamboo shoots if using.
Cook 400g ramen noodles according to the packet. Drain and divide between 4 bowls.
Strain the hot broth and add 2–3 tbsp tare per bowl. Ladle broth over noodles. Top with chicken, a halved soft-boiled egg, spring onions, and a drizzle of sesame oil.