Soften the marzipan by mixing in the kirschwasser. Add the sugar and egg yolks and place over simmering water. Whip until the mixture is light and fluffy. Remove from the heat, then continue whipping until cool.
Whip the cream to soft peaks. Fold the cream into the marzipan mixture.
Place in the freezer for at least 2 hours or, preferably, overnight.<