Thinly slice two medium onions and slice three green onions. Separate the white and green parts of the green onions—use whites for flavor and save greens for garnish.
2
Cut one pound of thinly sliced beef into bite-sized pieces.
3
In a small container, combine 1.5 cups water, 6 tbsp soy sauce, 6 tbsp mirin, 1 tbsp sugar, and 1 tsp hondashi. Mix well.
4
Pour the sauce into a large pot, add the sliced onions and green onion whites. Bring to a boil, then reduce heat to medium and simmer for about 2 minutes until onions become translucent.
5
Add the beef pieces and gently separate any that are sticking together. Cover and simmer for about 5 minutes until the beef is tender, adjusting time as needed depending on thickness.
6
Place rice in a serving bowl and top with the beef and onions. Add 1-2 tbsp of the braising liquid (use tongs or chopsticks to avoid oversaturating).
7
Garnish with green onion parts, pickled ginger, and a soft-boiled egg if desired.