(If no store near you carries ginger marmalade, use an equivalent amount of lemon marmalade mixed with 1/2 t ground ginger, or 1 T fresh grated ginger.) Put the whiskey, marmalade, lemon rind and sugar in a bowl. Stir well, then leave the mixture to stand for at least 15 minutes. Stir the cream slowly into the whisky mixture until evenly blended, then beat with an electric or rotary beater until thick. Beat the egg whites until stiff, then fold into the cream mixture until well blended. Spoon into 4 individual wine glasses or sundae dishes, then chill in the refrigerator for at least 30 minutes. Serve chilled, with brandy snaps or ginger snaps.