Many many years ago when I was working in a very old trading company in Osaka, old building, smoke stained walls, etc. At 17:00 we would always have a 15min tea break with a small snack provided by the company. (This apparently was to hold us over till our 21:00 dinner break)…these were the old days.

In the summer we all got a hard boiled egg, every day on rotation it was someone’s duty to take the eggs out an hour before so they warm up and wont crack, then we would put them in a plastic bag with a little tap water then submerge the bag in the potto with the top hanging out, close up the lid and in about 20 min we had a nice hard boiled egg with our tea. 15 min gets you a nice onsen tamago. 4 Seasons and 4 different treats, Spring pickles, Summer tamago, Fall baked sweet potatos & Winter baked omochi on the gas heater. We still try to carry on the tradition with the family now on the weekends in Sendai.
Be well, br, T