Cranberry Kiss

redcurrants,to garnish
1 egg white,lightly beaten,and 15ml/1 tbsp
 caster (superfine) sugar,to garnish
1 measure/1 1/2 tbsp cognac
2 measures/3 tbsp cranberry juice
2 measures/3 tbsp pink grapefruit juice
2 measures/3 tbsp marsala dolce