Onsen Tamago is a traditional Japanese way of cooking a slow poached egg. Traditionally, Japanese people would bring eggs to local hot springs heated by the volcanic activity on the island. They would put their eggs in the hot spring water and take them out 40 minutes later to have perfect Onsen Tamago or Hot Spring Eggs. (Salat) Debate of the perfect temperature ranges from 145 F and 160 F and the 15 degrees make a huge difference. 148-150 F is perfect for an extremely soft egg white and custard-like yolk.