Soaked in a strong spirit and then sweetened, currants transform into crème de cassis—an irresistible fruit liqueur essential to cocktails like the Kir Royale and El Diablo. This recipe, inspired by the house formula at Washington D.C.’s Black Jack bar, combines black and red currants, neutral spirit and rich syrup for a sublime liqueur that bottles up fresh-fruit flavors you can sip long after summer has passed.