Mousse Cake Chocolate Puffed Rice Base: I used Rice Krispies for the puffed rice, but any puffed rice cereal will work! The corn syrup is used as a liquid coating to make the puffed rice stick and malleable to form into the bottom of the springform pan. I use palm sugar as my sweetening agent for the crust because this is my preferred sugar. This sugar has both a low glycemic index and low fructose levels. It contains antioxidants, minerals, is unrefined, and contains no chemical breakdown alterations or artificial ingredients. It’s just pure and simple! I like to use bittersweet chocolate, which is 50% or higher cacao percentage.
Custard: The Base of the hazelnut mousse is a custard that is known in French terms as Crème anglaise. This delicate and fragile custard made with eggs yolks is combined with cream and heated over low heat until it has doubled in size and thickened. This custard is set with gelatin. This allows the cake to “stand up” and hold its shape and form.
Tempering the Milk with Egg Yolks: When the milk is heated and slowly added to the raw egg yolks and sugar, this is called tempering. The milk is hot, and the egg yolks are cold. Tempering means to slowly combine the two elements to bring them to a similar temperature. If the milk is added too quickly to the egg, the eggs will cook and scramble. Tempering allows the milk to slowly become incorporated with the raw egg yolks to make one combined mixture.
Cooking the Custard Mixture Over Heat: The custard has to be cooked over low heat and whisked constantly. Again, this mixture is quite fragile, as the base is egg yolks. If the mixture becomes too hot, the yolks will curdle and scramble. The custard is ready when it has doubled in size and thickened. This is when the gelatin is added to thicken the custard. The mixture is cooked another minute just until the gelatin has fully dissolved. Then the mixture can be taken off the heat.
Turning the Crème Anglaise into Hazelnut Mousse: While the crème anglaise is still hot, the hazelnut butter is added and whisked until it is evenly combined. The heat allows the butter to melt into the custard with more ease. The heavy cream is whipped to form soft peaks and FOLDED into the hazelnut custard. This folding is one of the essential steps. The soft and delicate whipped cream has been suspended with air molecules, and you do not want to break these molecules while mixing the cream into the hazelnut custard. The key to properly combining these two mixtures is to fold the cream into the custard in three separate additions. With each whipped cream addition, use a silicone spatula and glide your spatula through the center of the bowl. Then slide the spatula up and over, while simultaneously turning the bowl a ¼ turn. This process is repeated until all the cream has been added, and the mixture is one even and light toasted caramel color. If you pour in all the whipped cream at once and vigorously stir the bowl in circles, the whipped cream will deflate, and you will not have a light and airy mousse.
Dark Chocolate Ganache: Chocolate is also quite delicate and needs to be added to the cream properly to make a thick and smooth ganache. The heavy cream is heated just to a boil and poured over the chopped chocolate in a heatproof bowl. The heat of the cream slowly melts the chocolate. Let this mixture sit for 30 seconds to 1 minute before whisking. This mixture should be whisked until a smooth consistency is achieved. The room temperature butter is added to create a glossy shine and a more rounded finish.
Garnish: I love saving ¼ of the chocolate puffed rice mixture for topping the cake along with some rough-chopped toasted hazelnuts! I followed the look of Dominique Ansel’s cake and garnished these two elements on one side of the cake for a dramatic and stylized effect.
Chocolate Hazelnut Mousse Cake
Chocolate Puffed Rice Base
- 3 cups puffed rice
- 2 ½ tbsp light corn syrup
- 2 tbsp palm sugar
- 4 oz dark chocolate, melted
- 1 ½ tbsp unflavored powdered gelatin
- ¼ cup cold water
- ⅔ cup whole milk
- 5 large eggs, separated (use the yolksand save egg whites for another recipe)
- ½ cup palm sugar
- 1 – 1½ cups hazelnut butter
- 1 ⅔ cups heavy cream
Dark Chocolate Ganache
- 1 cup heavy cream
- 8 oz semisweet or bittersweet dark chocolate, chopped
- 2 tbsp unsalted butter, cubed at room temperature
- Chilled hazelnut mousse cake
- 1 recipe chocolate ganache
- ¼ recipe chocolate puffed rice
- ¼ cup hazelnuts, toasted and rough chopped
Chocolate Puffed Rice Base
- Preheat oven to 350 degrees Fahrenheit. Butter or spray a 9″ Springform pan.
- Place the puffed rice, corn syrup, and sugar in a medium-sized bowl and mix until the rice is thoroughly coated.
- Line a sheet tray with parchment paper or a silicone baking mat and spread the rice in one even layer on the pan.
- Place the pan in the oven and bake until the rice becomes golden brown, about 10-12 minutes.
- Take the rice out of the oven and place it in a medium-sized bowl and pour in the melted dark chocolate. Use a spatula to coat all the caramelized rice with the chocolate evenly.
- Press ¾ (reserve ¼ of the mixture to garnish the cake) of the chocolate puffed rice into the bottom of the springform pan. Use your hands to mold and shape the base into one even layer. Place in the refrigerator to firm-up and set while making the mousse.
- Place the gelatin and the cold water in a small bowl and stir until the gelatin has dissolved. Reserve.
- Place the milk in a medium saucepan and bring to a boil, just until bubbles start to form. Reserve.
- In a medium-sized bowl, whisk together the egg yolks and sugar. Slowly, pour in the hot milk a little at a time until the mixture is combined.
- Return the egg, sugar, and milk mixture back to the saucepan and cook over low heat, whisking the entiret ime until the mixture has thickened about 10-12 minutes. The custard mixture should be thick enough that it coats the back of a spoon.
- Stir in the gelatin mixture and cook an additional 2 minutes until the gelatin has dissolved into the custard.
- Take the custard off the heat and whisk in the hazelnut butter. Whisk until the mixture is evenly combined, and it is a thick and glossy toasted hazelnut color. Reserve.
- In a separate bowl, whip the heavy cream until soft peaks form. Fold the whipped cream into the hazelnut mousse in three additions, being careful not to break the air molecules of the cream. Repeat until all of the cream is folded into the mousse, and the mixture is evenly combined.
- Pour the hazelnut mousse into the chilled chocolate puffed rice crust and fill the springform pan. Use an offset spatula to scrape the top to make an even layer.
- Place the cake into the refrigerator and allow to set for 20-30 minutes.
Dark Chocolate Ganache
- Place the heavy cream into a small saucepan and bring it to a boil until bubbles start to form.
- Place the chopped chocolate into a heatproof metal or glass bowl and pour the hot cream over the chocolate. Let the mixture sit for 1 minute and then whisk until smooth.
- Add the butter to the chocolate and whisk until all the butter has dissolved, and the chocolate mixture is thick and glossy.
- Line a clean baking sheet with plastic wrap and place a cooling rack on top of the plastic.
- Take the hazelnut mousse cake out of the refrigerator and place it on the cooling rack. Very carefully, unlock and unmold the cake from the springform pan side, leaving the mousse cake sitting on the round base.
- Pour the chocolate ganache overthe cake and use an offset spatula to spread the ganache on top, evenly coatingthe whole cake. Use the spatula to get any spots on the sides of the cake thatyou missed. Repeat until the whole cake is evenly covered with the chocolateganache.
- Lift the cooling rack and cakefrom the sheet pan and place in the refrigerator to set for 10-15 minutes.
- Save the excess ganache onthe plastic wrap for another use:)
- Top the cake with thechocolate puffed rice and toasted hazelnuts.