A friend passed this to me from "Food and Wine." There is a similar recipe here on Food.com, but uses metric measurements. I don't have a kitchen scale, so I'm posting the English version, too!
Spoon the Nutella into a heatproof bowl. In a microwave-safe glass measuring cup, heat the cream at high power for 45 seconds or until very hot. Slowly whisk the cream into the Nutella until smooth and silky. Transfer to 8 small espresso cups and serve with biscotti.