Line six 125ml pudding moulds with clingfilm.
Heat whisky, currants, sugar, lemon zest, and ginger in a pan without boiling.
Strain the mixture through a fine sieve to extract juice and cool.
Whisk egg yolks and sugar over simmering water until pale and thick.
Remove from heat and continue whisking until the mixture is cool.
Mix 125ml of the cordial into the egg mixture one tablespoon at a time.
Fold in whipped cream, pour into moulds, and freeze overnight.
Macerate garnish currants in the remaining cordial overnight in the fridge.
Serve the semifreddos topped with the macerated currants.