- Place water, Japanese soy sauce, mirin and sugar in a saucepan. Bring to the boil over medium-high heat.
- Once boiling, remove from heat and add in bonito flakes. Leave for 20 mins, then strain through a sieve.
- Crack 2 eggs in a bowl, then whisk. Repeat with 2 remaining eggs in a separate bowl.
- In a small pot or pan, heat half dashi over medium-high heat. Add half the chicken and mushroom.
- Once chicken is cooked, pour over one bowl of whisked eggs. Sprinkle with half of the spring onions, then cover with a lid.
- Once egg is almost cooked, fill a bowl with rice, then transfer the egg, chicken and mushroom mixture onto the rice.
- Repeat with remaining ingredients.