1.To make the soup stock, place the bones in a large saucepan; add enough water to pan to cover bones. Bring to the boil; drain.
2.Rinse bones; return to pan. Snip kelp in several places using scissors; add to pan with onion, ginger, garlic, carrot and the water. Bring to the boil; discard kelp.
3.Place mushrooms in a small heatproof bowl, cover with boiling water, stand for 20 minutes; drain. Discard stems.
4.Cook noodles in a large saucepan of boiling water until tender. Add buk choy leaves to noodles at end of noodle cooking time; blanch for 20 seconds. Drain noodles and buk choy. Rinse under cold water; drain.
5.Bring soup, sauce and sake to the boil in a large saucepan.
6.Divide noodles and soup into bowls; top with mushrooms and remaining ingredients.
These Japanese wheat noodles are sold in dried, fresh, steamed and instant forms.