In a large bowl stir together all of the ingredients (except for the eggs) and set aside.
Fill a pot with a few cups of water over high heat and bring to a gentle boil. Reduce the heat if necessary so the boiling water isn’t boiling too hard.
Carefully add the eggs to the boiling water and cook for 6 minutes for a jammy yolk (a little runny in the center). If you prefer a firmer yolk then cook for 9 minutes. These cooking times will give you a nice balance of soft, rich yolks with slightly firm egg whites.
Gently remove the hard-boiled eggs from the pot of water and place them in a bowl of ice-cold water to stop the cooking process. After a few minutes in the ice water peel the cooked eggs. Don't worry if the eggshells come off a little rough—the marinade will hide any imperfections!
Take the peeled eggs out of the ice bath and put them into the miso marinade container. Make sure the eggs are fully submerged in the liquid. If needed, gently press them down with a spoon. Put the lid on and refrigerate the airtight container for at least 6 hours, but overnight is best for a deep, flavorful infusion.
Notes
These eggs will stay fresh in the fridge for about 5 days.
The nutrition data includes the values for the marinade ingredients, but the exact nutrition will vary by how much of the marinade is consumed.