CHOCOLATE MOUSSE WITH HAZELNUT PRALINE

Steps:

• Preheat the oven to 350 degrees F. Place the hazelnuts on a rimmed baking sheet and bake until toasted, about 10 minutes.
• Add the egg, egg yolks, vanilla extract, 1/3 cup sugar and 1 tablespoon water to a medium heatproof bowl and whisk to combine. Set the bowl over a medium saucepan of gently simmering water (do not allow the bowl to touch the water). Cook, whisking constantly and scraping down the sides of the bowl occasionally, until the mixture is pale, hot to the touch and has almost doubled in volume, 4 to 6 minutes. Remove from the heat and continue to whisk until the egg mixture has cooled, about 2 minutes.
• Put the bittersweet and semisweet chocolate in a medium heatproof bowl and set it over the saucepan of gently simmering water (do not allow the bowl to touch the water). Stir occasionally with a rubber spatula until the chocolate is melted and smooth.
• Meanwhile, whip the cream in a medium bowl with an electric mixer on medium-high speed until stiff peaks form, about 2 minutes. Set aside.
• Once melted, remove the chocolate from the heat and gently stir for about 3 minutes to cool slightly. (If it is too warm it won't combine with the egg mixture or the whipped cream without seizing up.)
• Very slowly stream in and whisk the chocolate into the egg mixture until combined. (The mixture may get very thick.) Using a rubber spatula, gently fold the whipped cream into the chocolate mixture in 3 additions until it is fully incorporated. Chill, covered, until firm, 4 hours and up to overnight.
• Meanwhile, line a rimmed baking sheet with a silicone baking mat. Add the remaining cup sugar to a small saucepan over medium-high heat. Melt the sugar, swirling the pan and stirring frequently, until it becomes a deep amber color, 4 to 6 minutes. Remove from the heat and fold in the hazelnuts. Pour onto the prepared baking sheet and quickly spread very thin. Let sit at room temperature until hardened, about 1 hour. Once hardened, transfer to a cutting board and finely chop.
• To serve, place the serving plates in the freezer until very cold, about 10 minutes.
• If using melted chocolate and whipped cream for serving, prepare them: Put the semisweet chocolate in a medium heatproof bowl and set it over the saucepan of gently simmering water (do not allow the bowl to touch the water). Stir occasionally with a rubber spatula until the chocolate is melted and smooth. Whip the cream in a medium bowl with an electric mixer on medium-high speed until stiff peaks form, about 2 minutes.
• Decorate the plates as desired with cocoa powder, melted chocolate or whipped cream. Place two spoons with deep bowls in a cup of boiling water. Remove the mousse from the refrigerator and spoon two quenelles onto each plate using the hot spoons (be sure to dry your spoons before forming the quenelles). Top with the hazelnut praline.