Transfer to a piping bag and portion into a 2.5-cm / 1-in diameter demi-sphere fleximold mat, smoothing out the top with an offset spatula. The molds should have at least 20 demi-spheres. Place in the freezer to harden.
Once hardened, fuse 2 sorbet demi-spheres together by rubbing the edges where they touch with your gloved hands. Return to the freezer.
Once hardened, insert a toothpick into each sphere. Dip each sphere separately into the melted chocolate shell. Keep inverted until all the excess chocolate has dripped off.
Insert the toothpick into a Styrofoam base to hold the spheres up while the chocolate sets.
Before the chocolate shell sets, sprinkle a small pinch of toasted hazelnuts on the chocolate.
Once the chocolate has set, remove the toothpick from the spheres and reserve them frozen, with the hazelnuts facing up.
Place a slice of the cake on the desired plate.
Sprinkle a pinch of Maldon sea salt on top of the cake.
Place a sphere next to the cake, with the hazelnuts facing up.
Temper the entire dessert for 4 to 5 minutes before serving.