Place the blackcurrants, sugar, cassis liqueur and grated ginger in a small saucepan and simmer over a moderate heat until thick and syrupy. Spoon the blackcurrant mixture into a gratin dish.
In a clean, grease-free bowl, whisk the egg whites until stiff peaks are formed when the whisk is removed.
Gradually add the caster sugar to the egg whites, one tablespoon at a time, whisking continuously until the mixture is thick and glossy.
Fold the vanilla seeds into the egg whites and mix well to combine.
Place the egg white mixture on top of the blackcurrants to cover completely.
Brown the meringue with a mini-blowtorch until it is golden-brown all over. Serve immediately.