Flourless Nutella Chocolate Cake

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

• Ready In: 1 hr 10 mins
• Serves: 8
• Yields: 1 cake

Ingredients

• 200  g unsalted butter
• 100  g dark chocolate
• 200  g  nutella
• 100  g sugar
• 6  eggs, separated
• 1  teaspoon  espresso powder

Directions

1. Preheat the oven to 350F / 175C, and place your baking rack on the lowest rung.
2. Butter and lightly coat a 9″ springform pan with unsweetened cocoa powder.
3. 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.
4. 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.
5. Beat the egg whites in mixer bowl until peaks start to form to moderately stiff peaks.
6. 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.
7. 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).
8. 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.
9. Let the cake cool completely, at least 30 minutes before serving. It'll likely deflate quite a bit.
10. Can serve plain or with whipped cream and/or berries.