For the blackberry and elderberry jam, boil the blackberries, the elderberries and 100 g of jam sugar together until the fruits are soft.
Allow to cool a little and strain with a slotted spoon.
Add the remaining 200 grams of jam sugar with the juice and zest of one lemon to the pot and boil for another 5 minutes.
Fill the hot blackberry jam into 6 jars, depending on the size.
Preparation Tip:
Turn the jam jars upside down after filling, this will prevent oxygen from getting into the jars. This makes the jam last longer and reduces the chance of mold.