Fill a 4 quart saucepan half full with water and bring to a boil. Place you eggs onto a large slotted spoon so you can gently lower them into the boiling water. When the water boils, add about 1 tsp of salt – a generous pinch – as you lower the eggs into the water (the burst of bubbles the salt releases helps to cushion the eggs and prevent cracking). Set a timer for 6-6 ½ minutes (depending on if you want a runny or jammy textured yolk) and reduce heat to maintain a gentle simmer. While the egg cooks, prepare and ice bath. When the eggs are finished cooking transfer them immediately into the ice bath to stop the cooking and allow them to cool completely.  Meanwhile, make the marinade.
 
Combine the soy sauce, mirin, rice wine vinegar, water and sesame oil (if using) to make the marinade and pour into a sealable plastic bag. Carefully peel the eggs (don’t forget that they are soft!) by cracking the shells all over and peeling under a gentle stream of water will help to neatly remove the peel. Place the peeled eggs into the bag with the marinade and seal the bag, pressing out as much excess air as possible so that the eggs are completely submerged in the marinade. Refrigerate overnight, or up to 36 hours – the longer the egg stays in the marinade the more intensely it will take on the flavor. Remove eggs from the marinade and use immediately or store in the refrigerator for 3-4 days. Marinade may be reused a second time. 
 
Use to top your favorite ramen bowl or as a delicious snack on their own. We enjoyed them with a dab of wasabi or sriracha sauce or a sprinkle of furikake.
 
* We found that rice wine vinegar helped to both brighten the flavor and intensify the color of our ramen eggs. Sesame oil added another layer of flavor we enjoyed as well. If you prefer a milder flavor use water in place of half of the vinegar. If you are rushed for time, cut the vinegar in half for a quick marinade that is ready in 4-6 hours.