Blanch the pork bones in boiling water for 10 minutes. Drain, rinse under cold water and discard the blanching liquid.
Place the blanched bones, garlic, ginger and spring onions in a large pot. Add 2 litres of fresh water. Bring to a vigorous boil.
Reduce to a strong simmer and cook uncovered for 2.5 hours, adding water to keep the bones submerged. The broth should turn milky white and creamy.
Remove the pork belly after 1.5 hours (it should be tender). Slice and set aside for topping.
Strain the broth through a fine sieve. Season with the soy sauce, mirin and sake. Adjust to taste.
Cook the ramen noodles according to package instructions. Drain.
Divide noodles into bowls. Ladle the hot broth over. Top with sliced pork belly, a halved marinated egg, nori, bean sprouts, spring onions, bamboo shoots and sesame seeds.