Prepare a syrup by boiling 100g sugar in 50ml water to the soft-ball stage. Whisk together 1 egg and 5 yolks. Add the syrup slowly in a thin stream, whisking until cold and thick.
Whip 500 ml double cream until it stands in soft peaks. Fold this into the egg and syrup mixture, making sure that all the ingredients are thoroughly mixed before proceeding to the next step.
Tape collars of non-stick parchment around four 8 cm metal rings, ensuring they rise 2 cm over the rims. Stand the rings on a baking sheet lined with parchment and pour in the mixture to the height of the collars.
Level the surface with a palette knife and freeze until firm. The parfaits are easily unmoulded by briefly wrapping a hot tea-towel around the rings once the collars are removed.