Mix the juices - I always take the finished elderberry juice from the bottle - in a saucepan and bring to the boil with the preserving sugar for 3 - 4 minutes.
Also works very well with Gelfix if you have normal sugar instead of preserving sugar. (According to package instructions!)
Just before pouring in the calvados, I have already tried that with amaretto, which is also great. Can simply be left out if children are to eat or if you do not want to take alcohol.
Immediately pour into glasses and turn out, let stand for 10 minutes.