Briefly rinse the currants with cold water and drain well. Put the berries in a large bowl, mash them, pour the red wine over them and marinate covered for 2 days.
Then bring the berries to the boil in the wine and filter through a paper coffee filter or cloth and drain well.
Bring the liquid with the powdered sugar to the boil, remove from the hob and let cool down a little. Then stir in the schnapps. Fill and seal the liqueur in sterilized bottles. Store in a cool, dark place.
For a Kir Royal, put 20 cl cassis in a champagne glass and fill up with 150 ml ice-cold champagne.