Blueberry-Apple Cordial

To make the cordial, combine blueberries, lemon zest and brandy in a tightly sealed jar and allow it to marinate in a cool, dark place for a month, shaking daily to mix the flavours.// When it is time to make the cocktail, strain the cordial through a cheesecloth into a bowl and add simple syrup to sweeten. Chill for half an hour. Pour the cordial into a flute and top with sparkling wine, then serve.