Combine the Ingredients
In a small mixing bowl, blend the Japanese soy sauce, mirin, and kombu. Stir gently to allow the flavors to meld.
Add the Egg Yolks
Carefully place the egg yolks into the prepared soy sauce mixture, ensuring they remain intact. Cover the bowl and refrigerate to allow the yolks to cure. Depending on your preference, marinate them for a minimum of six hours or extend the process to two or three days. During this time, the yolks will darken and become firmer, with a creamy texture achieved at around 8 to 9 hours.
Serve
Present the yolks over steamed short-grained rice, using one to three yolks per serving as desired. The dish is best enjoyed fresh to appreciate its balance of flavors and textures.
Tip
For a traditional pairing, opt for short-grained rice, which complements the richness of the yolks while enhancing the dish's authentic Japanese character.