Gently lower large eggs into a pot of water heated to 65 degrees Celsius. Maintain this temperature for 25 minutes. Remove large eggs and plunge into an ice bath to stop cooking.
2
Slit the mentaiko sacs lengthwise and scrape out the roe into a bowl. Add unsalted butter, koikuchi soy sauce, mirin, sake, and dashi stock to the mentaiko. Mix thoroughly until well combined and creamy.
3
Finely chop the scallions. Shred the nori into thin strips.
