Onsen tamago (温泉卵 or 温泉玉子) is a traditional Japanese boiled egg which is originally slow cooked in the water of onsen hot springs in Japan. The egg has a unique texture that the white tastes like a delicate custard (milky and soft) and the yolk comes out firm, but retains the color and creamy texture of an uncooked yolk. The special texture is cooked by using the difference between the temperature of which the egg yolk and egg white solidifies. The egg is poached within the shell and is served with the shell removed in a small cup with sauce of broth and soy sauce [ref]. Those were from Kusatsu Onsen in Gunma and were delicious !