shichimi togarashi chilli powder (optional, available from Asian supermarkets or online)
In a saucepan, bring the soy, mirin, sake, vegetable stock and sugar to the boil. Let simmer for a few mins, then add the onions. Cook for 10 mins until brown. Add the steak and simmer for 5 mins on a medium heat.
Rinse the noodles and drain. Add to the meat and broth, and cook for 5 mins. Serve with rice, pickled ginger, spring onions and a little chili powder, if you like.