Bring the blackberries with water and rock candy to the boil, after cooling through the Flotte Lotte twist or puree, then fill up with the grain. Personally, I rub the mass through my Rösle sieve (is particularly fine) and then fill it up in bottles.
Also tastes great in sparkling wine or cava.
It is easy to add or reduce, as the amount remains the same, e.g .: 500 g blackberries, 500 g rock candy, 0.5 L grain and 0.5 L water.