Whisk the egg yolks, sugar and vanilla sugar with the whisk of the hand mixer for 5-8 minutes until thick and creamy. Stir in chestnut cream. Whip cream until stiff and fold in. Freeze the mixture for 40-45 minutes.
Chop the couverture and melt in a hot water bath. Let it cool down a little. Using a fork, quickly stir the liquid chocolate glaze into the frozen chestnut cream with a fork (the glaze will quickly set).
Pour the chestnut mixture into the moulds or cups. One after the other, sprinkle with the rest of the couverture and pull it through lightly with a fork at the top. Cover with foil and freeze for about 2 hours. Let thaw for 20-30 minutes, then serve.