1. With an electric mixer on medium-high speed, whisk cream until soft peaks form. Transfer to refrigerator; chill for 1 hour.

2. In a clean mixing bowl, and with a clean whisk, beat yolks on high speed until pale and frothy. Meanwhile, bring sugar, corn syrup, and water to a boil in a small, heavy saucepan over high heat, stirring to dissolve sugar. Continue boiling for about 1 minute. With mixer on medium-low speed, carefully pour hot syrup down side of bowl. Beat on medium-high speed until slightly thickened, about 5 minutes. Beat in hazelnut praline paste. Stir in chocolate, vanilla, and a pinch of salt with a flexible spatula.

3. Add one-third of the chocolate mixture to whipped cream; whisk to combine. Add remaining chocolate mixture, fold to completely combined. Pass through a coarse sieve into a large bowl; discard any solids.

4. Transfer mousse to a disposable pastry bag or large plastic bag. Using scissors, snip a small hole in bottom of the bag or from one of the corners of the plastic bag. Pipe mousse into chocolate cups to fill; serve garnished with hazelnuts and shaved chocolate.