- 01
In a small saucepan, add the mirin, sake, and sugar, stir, cook over medium heat, and stir to combine. Add the soy sauce and cook until boiling.
- 02
Lower the heat until simmering. Simmer for 10-15 minutes or until the sauce is 1/3 of the original volume. Take off heat. If the sauce ends up too thick, dilute it with some water. If the sauce is not thick enough, cook it some more.
- 03
Cut the unagi fillets into two or three pieces, depending on the size of the donburi bowl. They should fit it nicely, without having to fold them.
- 04
If you wish to broil the eel, set your broiler to 550ºF/288ºC and heat it for 5 minutes. Place an oven rack about 8 inches (20 cm) away from the top heating element. Line a baking tray with tin foil, then lightly coat it with oil to prevent sticking. Arrange the unagi fillets on the baking tray skin-side down. Broil for 5-7 minutes until bubbly on top, then brush with the unagi sauce and broil for another 30-60 seconds.
- 05
If you wish to prepare it in the oven, follow these instructions. Set the oven to 425°F/218ºC and position the oven rack in the middle of the oven. Line a baking tray with grease paper and arrange the unagi fillets on it. Bake for 10-12 minutes, then brush the top of the fillets with unagi sauce and bake for another 30-60 seconds.
- 06
If you wish to prepare the fillets in the pan, first, cut out two 16 x 16 inch (40 x 40 cm) pieces of aluminum foil. Lightly grease one side of the foil. Place two fillets in the center of each piece of foil. Fold the foil to enclose the fillets, shaping it into a pouch. Arrange the pouches in the pan and cook over low heat for 5-8 minutes.
- 07
Fill a donburi bowl with steamed rice. Brush the top of the rice with the unagi sauce. Top with the the unagi fillets and brush the fillets with unagi sauce. If desired, sprinkle with ground Japanese sansho pepper.