Place the egg yolks in a heatproof mixing bowl.
Add 40g sugar and the vanilla.
Add the vanilla to the egg yolks.
Whisk until frothy.
Heat 80ml water in a pan.
Add the remaining sugar.
Heat until the sugar has completely dissolved.
Set the bowl with the egg yolk mixture over a pan of hot water. Add the sugar syrup and stir until the mixture thickens.
Whip the cream to soft peaks.
Stir the vanilla cream over a bowl of iced water until cold.
Fold in the whipped cream.
Spoon the parfait mixture into small bowls and freeze for 5 hours. Thaw briefly before serving. Turn out before serving if desired.