1Prepare the onsen tamago: Bring a pot of water to a boil, then turn off the heat. Carefully place the eggs into the hot water, cover the pot, and let them sit for 15-18 minutes. Immediately transfer the eggs to an ice bath to stop the cooking process.
3Prepare the tare: In a small bowl, combine the koikuchi soy sauce, mirin, rice vinegar, sesame oil, granulated sugar, grated garlic, grated ginger, and dashi stock. Whisk until the granulated sugar dissolves completely.