Gather all the ingredients.
You can keep the onsen tamago for 1-2 days in the refrigerator. To reheat, take out the onsen tamago from the fridge to room temperature. Place it in 160 ºF(70 ºC) water for 10 minutes to warm up. Do not reheat higher than that otherwise the egg will be cooked.
Equipment you will need:
Recipe by Namiko Chen of Just One Cookbook. All images and content on this site are copyright protected. Please do not use my images without my permission. If you’d like to share this recipe on your site, please re-write the recipe in your own words and link to this post as the original source. Thank you.