Preparation

To make the mousse:

• In a 2-qt. metal bowl set over a saucepan of simmering water, melt the chocolate, stirring with a rubber spatula until the chocolate is completely smooth. In a separate small saucepan, heat 1/2 cup of the cream over medium heat to just below the boiling point. Remove the bowl of chocolate from the pan of water and wipe the bottom and sides dry. Pour the hot cream into the melted chocolate and stir together with the spatula until well blended. Add the hazelnut butter and stir until well combined. Stir in the 2 tsp. vanilla.
• 在一个冷藏的搅拌碗中，使用冷冻搅拌器打败剩余的1杯奶油，直到其保持柔软的峰。用橡胶刮刀将鲜奶油折叠到四批巧克力混合物中，每次添加后都会彻底混合。将慕斯倒入1-1/2 QT中。蛋奶酥碟或碗，或放入单独的碗或眼镜中。用保鲜膜覆盖并冷藏直至设置，至少2小时（如果使用它来填充Profiteroles）。
  

To make the garnish:

• In a chilled mixing bowl with chilled beaters, beat the 1/2 cup cream until frothy. Add the 1/2 tsp. vanilla and continue beating until the cream holds soft peaks. Pipe or spoon the whipped cream on top of the mousse. Sprinkle the chopped hazlenuts over the whipped cream and serve.

Make Ahead Tips

This mousse is best when served within 6 hours of the time it’s made.