Drain the cherries and put 100 ml (3½ fl oz) of the syrup into a small saucepan. Stir the cinnamon, vanilla extract and sugar into the syrup and heat for 5 minutes or until the sugar has dissolved. Set aside to cool.
Stir the egg yolk through the crème fraîche. Add the drained cherries to the syrup, then mix in the crème fraîche. Fold the meringue nests carefully through the mixture.
Transfer to a 300 ml (½ pint) freezerproof container and freeze for at least 4 hours. Eat within a day when the parfait will be softly frozen. Decorate with fresh cherries before serving.