Whisk the egg yolks and sugar in a thin-sided bowl. Suspend over a gently simmering bain-marie; the bowl must not touch the water. Using the whisk on a mixer, beat until the mixture is light and frothy. Remove the bowl, continue to beat until the mixture is cold. Fold in the sour single cream. Beat the egg whites with the salt until stiff, carefully fold into the mixture, transfer to the prepared tin, cover and freeze for approx. 4 hrs.
Bring the espressos and sugar to the boil in a small pan, turn down the heat and reduce the liquid to approx. 100 ml, leave to cool.
Mix the grapes with the Marc de Champagne, toss in sugar. Cut the parfait into slices, serve with the coffee sauce, grapes and amarettini.