These will keep for a month in the fridge therefore I make a batch to add to ramens on rice dishes. I use Japanese tamari soy sauce as this has the benefit of being gluten free. If you can't get hold of it, use light soy sauce instead.
Place all the marinade ingredient in a saucepan. Bring to the boil, simmer for 5 minutes. Remove from the heat and allow to cool completely.
Bring a large pan of water to the boil. Prepare a bowl with iced water to cool the eggs once cooked. Working in batches of 4 eggs at a time, cook the eggs for 7 minutes. Remove and plunge into ice bath.
Once all the eggs are cooked, carefully peel them. Submerge into the cooled marinade and leave for 6 hours. Remove from the marinade, either use straight away or store in an airtight container for 1 month.