Trim and slice chicken into thin strips.

Mix together broth, fish sauce, soy sauce, mirin, and sake, and stir in sugar until dissolved. 

In a pan, spread out a layer of onion and pour over that enough sauce to cover it. Add a layer of chicken pieces. 

Bring broth to a boil, lower heat, and simmer until chicken is cooked. 

Drizzle some beaten egg over the chicken, cover, and continue simmering until the egg is cooked but still a bit runny. 

Pour chicken and egg over steamed rice. Top with chopped scallions.