From http://www.msadventuresinitaly.com/blog/2011/02/05/flourless-nutella-chocolate-cake-recipe-for-world-nutella-day-2011/ Am posting here so I can convert grams to US
Preheat the oven to 350F / 175C, and place your baking rack on the lowest rung.
Butter and lightly coat a 9″ springform pan with unsweetened cocoa powder.
Cut the butter and the dark chocolate into chunks (or use high quality dark chocolate chips) and melt in a double boiler or in the microwave (on very low power) until smooth.
Remove butter/chocolate mixture from heat source and add the Nutella and mix well with a small whisk or fork. Add the espresso powder and mix inches.
Beat the egg whites in mixer bowl until peaks start to form to moderately stiff peaks.
In a large mixing bowl, add the sugar to the egg yolks and beat with a whisk until thoroughly incorporated. Add the chocolate mixture and mix inches.
Carefully add in the egg whites into the rest of the mixture and stir until well-blended (try not to deflate the egg whites completely but make sure they’re completely mixed in).
Pour into the prepared springform pan and place into the oven. Bake for 20-30 minutes. The cake should still seem a little "jiggly" in the center but a toothpick should come out clean.
Let the cake cool completely, at least 30 minutes before serving. It'll likely deflate quite a bit.
Can serve plain or with whipped cream and/or berries.