Cut the onion into 3mm thick slices, cut the leek diagonally, and the beef into bite-sized pieces.
Stir fry the onions and leeks in oil until soft, using a fairly generous amount of oil.
When the onions and leeks are softened, add the beef and stir fry.
Add water and bring to a boil. Add sugar and simmer for about 5 minutes.
Add the mirin and mentsuyu and simmer for about 10 minutes.
Adjust the taste with soy sauce.
Put over the rice in a bowl. Use as much sauce as you like. Top with red pickled ginger and serve.
Story Behind this Recipe
My husband likes leeks in his gyudon and I like onions in mine. So I used both!
If you don't have both onions and Japanese leeks, just use one. Use more onions to make the dish sweeter, and leeks to make it more salty. Adjust the flavor with sugar and soy sauce to taste at the end.