Onsen Egg

Ingredients

• 1 chicken egg

Method

The onsen egg is a study in temperature-control. At 70°C, the egg white sets whilst the yolk stays runny — a narrow window where the proteins in the white denature faster than those in the yolk. This is not guesswork: egg white coagulates at 63°C, the yolk at 65°C, but the rate matters. Hold 70°C and you're cooking the white at speed whilst the yolk lags behind, still fluid at the centre.

Fill a pot with enough water to submerge the egg by 3 cm. Use a probe thermometer — not a dial, which won't track the precision you need. Bring the water to exactly 70°C before the egg goes in. This is crucial: if you add a cold egg to hot water, the temperature will spike and crash as it equilibrates, cooking the yolk too far. Set the heat to maintain 70°C dead steady. No variation.

Lower the egg into the water gently. If you're cooking more than one, space them so they sit on the bottom without touching — moving water around each egg ensures even gentle-heating. Set a timer for 25 minutes. The water should barely shimmer; any rolling boil means your heat source is too aggressive and you've lost temperature control. Check the thermometer every five minutes and adjust the burner down if it creeps past 70°C.

Whilst the egg cooks, fill a bowl with ice and cold water. At 25 minutes, lift the egg out with a spoon and submerge it immediately in the ice bath. The shock stops the cooking dead. Wait three minutes — this allows the residual heat to dissipate fully without further cooking the yolk.

Crack the egg into a serving bowl. The white will be set and delicate, barely holding together; the yolk will break and flow like sauce. Serve at once with soy sauce, a pinch of sea salt, and toasted nori if you want it, though the egg itself is the point.