Preparation

• Whisk together the soy sauce, mirin, sake (if using), water, and sugar in an airtight container until the sugar is fully dissolved. Set this marinade aside.
• Bring a medium pot of water to a rolling boil and prepare an ice bath in a separate bowl.
• Carefully lower the eggs into the boiling water and set a timer for 6 minutes and 30 seconds.
• Immediately transfer the cooked eggs to the ice bath and allow them to cool completely for 5-10 minutes.
• Gently tap and roll each cool egg to create tiny cracks, then peel them under cold running water or in the ice bath.
• Place the peeled eggs into the prepared marinade, ensuring they are fully submerged. If using a bag, remove excess air.
• Refrigerate the eggs in the marinade for at least 6 hours, or ideally overnight (12-24 hours), turning occasionally for even flavoring.
• Remove the eggs from the marinade, slice them in half lengthwise, and optionally drizzle with marinade before serving.