Drop-lidotoshi buta, substitute: aluminum foil or parchment paper with several half inch holes
Let’s prepare the saba, mackerel fillet. With kitchen tweezers, remove the small bones from the middle of the fillet.
Flip the mackerel over, cut it in half and make a shallow diagonal cut in the skin of each piece.
Add water to a large amount of boiling water to bring it just below the boiling point. With a mesh strainer, submerge a piece of mackerel into the hot water. When the surface turns white, immediately drop it into a bowl of ice water. Repeat this process for the other piece of mackerel.
Gently rinse the surface of the fillet and remove the moisture thoroughly with a paper towel. This process will help remove the fishy smell and clean the surface.
Let’s simmer the mackerel. Combine the water, sake, sugar and mirin in a pan. Dissolve half of the miso in a ladle and then distribute it into the mixture. Turn on the burner and bring it to a boil.
Place the fillet into the miso sauce with the skin side facing up. A pan or shallow pot is easy to use when simmering fish. Bring the sauce to a boil again and remove the foam with a mesh strainer.
Drop in the ginger root slices and the green part of the long green onion. The onion will help cover the fishy smell.
Place the dampened wooden drop-lid called otoshi buta onto the fillet to help it cook evenly. Simmer for 5 minutes on medium heat.
Uncover and remove the long green onion. Ladle the broth into a bowl and dissolve the rest of the miso and then distribute it back into the pan. Adding the miso in 2 steps will help prevent the miso from losing its aroma.
Add the bell pepper, cover and simmer for 2 to 3 more minutes.
Uncover and remove the bell pepper before it fades in color. Ladle the miso sauce over the fillet and reduce the sauce without the drop-lid.
Turn off the burner and place the fillet onto a plate. Put the bell pepper next to it and ladle the miso sauce over the mackerel. Finally, garnish with the shiraganegi, the shredded white part of the long green onion.
For the drop-lid you can substitute aluminum foil or parchment paper with several half inch holes. In that case, you should place some kind of small weight on top, for example a light plate.