Wash the berries well and then drain. Remove the Elderberries from their branches/twigs by stripping them off with a fork.
Put both lots of berries into a large saucepan and cook over a low heat until they turn to a soft pulp. Press the berries as they cook to speed the process along and to extract as much juice as possible. If you are using very ripe berries, proceed to the next step. If the berries are still holding their shape or are not very juicy, you can blend them quickly at this point.
Rub the pulp through a sieve using the back of a spoon or the back of a ladle. The aim is to extract the juice and leave behind the seeds.
Very Important; measure the resulting juice. To each 600ml of juice add 450g of jam sugar and 1 tablespoon of lemon juice. You may not need all the sugar that you have set aside for this recipe.
Heat the juice/sugar/lemon until the sugar has dissolved then turn up the heat and boil rapidly until setting point is reached.