For the blackberry-raspberry jam, place the berries in a saucepan and chop using a hand blender. Add the berry preserving sugar and a squeeze of lemon juice and bring to a bubbling boil for three minutes.
Fill a long container with about 1 cm of hot water. Pour the jam into jars using a funnel.
Close the jars and place them upside down, with the lid first in the hot water, so the vacuum is formed and the jam lasts longer.